Construction for a traditional shape travel trailer...

[mdk]

A number of years ago, about the time I first saw foamular in the Home Depot, I had the inspiration to build myself a low, somewhat aerodynamic travel trailer, using foam and 1/8 inch lauan to skin it, and using some hardwood plywood and small dimension standard lumber to build a super-light small travel trailer ( standing room and FSC) to tow with a minivan. But since then my needs and wants have changed ( very much permanently) to something that's durable and intended for backcountry use... Death Valley, Mohave desert, off-road, dirt road, and of course, normal TT camping.

But I'm still interested in saving weight, as much as possible, because the less the "box" weighs, the more I can put inside and still remain on target, and I now want to have at minimum 50 and more likely 70-80 gallons of water, adequate holding tanks, and good battery power, for extended "no services or facilities" adventures, be it the southwest, rockies, or perhaps even north slope of Alaska, Northwest Territories, and wherever else the spirit might lead. And I want to stay under 2800 lbs, wet. It means doing a lot of non traditional things, like different source for heat and cooling, perhaps a tankless water heater, and other "not normal rv outfitting" types of things. And I want to cover most of the roof with solar panels.

My technique for construction, was to use 1/8 and some 1/4 inch plywood skin, bonded to the foam, to build some framing into the the foam, somewhat like they make the house kits out of sheathing bonded to styrofoam and framed at the perimeters, assembled in sections. Even using double strips of 3/8 or 1/2 inch hardwood plywood bonded ( with something like Gorilla Glue) into at least three layers instead of dimensional lumber, it's just more resilient and less likely to break due to stress and bending, etc.

Since I am no artist, I can't draw this for you, but in the end, it's assembled on the trailer, and once glued and screwed, you should be able to even flip the darn thing and it refuse to fly apart, unless a car drives through it or something.

Since I see others experimenting, I figured it's always smarter to learn from what others have done... I have spent some time looking through the forum and sadly, this forum has SO much information, that I ended up with overload and endless sidetracking by non-relevant but fascinating stuff. I'm hoping to reach a few of you who have or want to go down this path, and see if we can't share info and ideas...

I don't even know where to start, really. So, I'll let you all weigh in on whatever you think.

[atahoekid]

Don't worry MDK. We know the long thread is way too long to digest. There's good stuff there but we keep making left turns to talk about dogs, kids, cats, beer and dogs again. There are also a lot of other threads that discuss things like glue and cutting methods, you might find those more useful. But it seems to me that you're essentially on the right track. You can think of the walls as structural panels. Foam core (the formular you mentioned is perfect) with an inner skin of plywood or luaun (I'm using 5mm) and an outer protective skin of a fabric of some sort (canvas, fiberglass, bed sheets, even aluminum). If you're interested in some additional strength and depending on how large your build, a couple of bulkheads in the foam of cabinetry can be inserted and act as an anchor points and an inner skeleton. Hard attachment points (plywood blocks) inserted into the panels allow for mounting of doors, windows. lights, hatches and other fittings. There are examples of off-frame builds where the cabin is mounted to the frame upon completion of an entire shell. Anyway, keep asking the questions. We're a pretty helpful bunch and we'll make sure you don't end up re-inventing the wheel. Just ask as you start considering methodologies or materials and we're sure to give you our two cents worth. Lots of different ways to get this done, and it's possible that you could provide ideas that no one else has yet to consider. Welcome Aboard!!

[eaglesdare]

i don't think i could have said it any better. so ditto

welcome to the foamie section. ask away.

[pete42]

MDK
I want to stay under 2800 lbs, wet Weight of 1 US Gallon of water = approx. 8.35 lb
50 gallons X 8.35 = 417.5 #
60 gallons X 8.35 = 501 #
70 gallons X 8.35 = 584.5
80 gallons X 8.35 = 668 #

it would require some big tanks think 55 gallon drum size
I don't dry camp so the knowing how much water is needed is not in my knowledge base.
I'm sure you know what is needed I just wanted to remind you how much water weighs

pete

[GPW]

I’d think if you want to carry this much water , it would be better to spread it out .. smaller containers in different locations , according to the load and balance ... ... and what about the Beer ....

[Wobbly Wheels]

Glen's right about the tankage - spread it out. In boats, we break up the tanks as much as possible to use dead space in the hull like the keel stub and hull sides.
Our design requirements are similar in that I want to be self sufficient (for about a week at a time) but 2800lbs is too much weight for me to tow (even half that is pushing it.) Only about a third of my camping is in semi-arid terrain, so my tankage is also less. I will be towing over logging road with waterbars (shallow cross ditches) so I need to have at least the same ground clearance as my truck.

The first idea that comes to mind right away are a steel frame like how SawtoothXJ built his trailer. Are you thinking along the lines of a TD or do you want standup height ? I'm guessing that overall height is not a limiting factor for you ?
A steel frame, if it's within your skillset, will allow you to build a tough skeleton and glue/screw foam and ply to close it in and will also allow structural hardpoints to carry things like a spare, jerris for gas and water, jackall, boat externally to save interior space. Plus, you'll get that extra weight off the tow vehicle's suspension. What is the new tow vehicle ? (I'm assuming it's not a minivan...)

The other thing that occurs to me is that you may want to incorporate your water tank into the floor. Once you've figured out your floor area, you can build it up with a false floor and build a baffled tank 4-6" high. This will spread your water's weight over the whole trailer's area and will keep it as low as possible. It can also be partitioned for separate fresh and grey water tanks. I've built some strong diesel, water and waste tanks out of epoxy and ply - it's easy to do, even if you've never glassed before.

Personally, I'd avoid all foam construction for your particular (offroad) use. I thought over this one for a while - the puncture resistance of ply vs its weight. A was concerned about branches trashing the foam since I drag my truck through to bush to hunt, fish, and camp. Many of the dents and scratches on my truck would have resulted in chunks of fam being pulled out of a trailer's sides and top...I chose to glass over foam, but I'll be carrying a repair kit and glassing is something I'm familiar with. So I guess the obvious question is: what are your own skills and strengths ?
There are plenty of ways to skin this cat....

[mdk]

As for the weight of water... Yes, sadly, I'm very aware of that. My first travel trailer had BOTH the fresh and holding tanks behind the axles, - holding was back against the rear bumper- and it towed like a wiggly snake, especially when the holding was almost full.
The only practical space for the fresh would be the under the bed, and I'm intending for that to be at the front. Since I'm going to have a frame that's almost 2 feet off the ground, it's my intention that the holding tanks go right above the back axle - one for black and one for gray. I intend to have the freshwater tank inside the insulated space.. and am trying to figure out how to insulate the holding, too, so that adventures into below freezing weather are possible and workable. Exposed tanks in very hot weather tend to get you warm, nasty water, when the heat off the pavement heats it up. It may be possible to put the fresh water tanks into the same kind of insulated pocket as well near the axles, but I'm having difficulty figuring out how to put heat from inside into the space to warm it, not to mention, having a convoluted filler... And at the same time, I want to avoid the weight of a conventional rv furnace and ducting.

Oh, almost forgot... NO BEER. We don't drink alcohol... Nor coffee. Nor soda.

So the refrigerator has to be kinda big, too. I'm a vegetarian.

[mdk]

Don't worry MDK. We know the long thread is way too long to digest. There's good stuff there but we keep making left turns to talk about dogs, kids, cats, beer and dogs again. There are also a lot of other threads that discuss things like glue and cutting methods, you might find those more useful. But it seems to me that you're essentially on the right track. You can think of the walls as structural panels. Foam core (the formular you mentioned is perfect) with an inner skin of plywood or luaun (I'm using 5mm) and an outer protective skin of a fabric of some sort (canvas, fiberglass, bed sheets, even aluminum). If you're interested in some additional strength and depending on how large your build, a couple of bulkheads in the foam of cabinetry can be inserted and act as an anchor points and an inner skeleton. Hard attachment points (plywood blocks) inserted into the panels allow for mounting of doors, windows. lights, hatches and other fittings. There are examples of off-frame builds where the cabin is mounted to the frame upon completion of an entire shell. Anyway, keep asking the questions. We're a pretty helpful bunch and we'll make sure you don't end up re-inventing the wheel. Just ask as you start considering methodologies or materials and we're sure to give you our two cents worth. Lots of different ways to get this done, and it's possible that you could provide ideas that no one else has yet to consider. Welcome Aboard!!

I figured out the strengthening behavior of having internal walls long ago. I once tore the insides out of an aluminum trailer, thinking it would get light... Nope. The thing was built like a tank. But with the interior gone, the coachworks flexed and flopped in the wind like a kite.

As for the outside skin. The purpose of using plywood, rather than foam or fabric, was the puncture resistance. And I'm intending to completely paint the outside with a waterproofing urethane - something that's UV resistant, and then paint the color or colors I want over that. A while back, I found some metalicized urethane weatherproofing stuff, it looks like the old silvery roof sealant, but instead of being like tar and drying out, the testing showed that you could paint plywood with it, submerge it under water for extended periods, and it would prevent even dampening of the plywood. And the sun won't rot it, because it has the metal flakes that totally block all light. It'll take me a while to find it. You can then paint over that, if you wish. (not sure I want a not quite shiny metalicized silver exterior!)

[atahoekid]

Just a thought here MDK... since you want to use plywood on the outside, how about skinning the inside with a fabric. Same structural panel just flipped inside out. Lots of thinking and playing with different materials going on around here. Best thing to do is try a small scale experiment with it and see if it does what you want. Never know till you try it!!!

[mdk]

Just a thought here MDK... since you want to use plywood on the outside, how about skinning the inside with a fabric. Same structural panel just flipped inside out. Lots of thinking and playing with different materials going on around here. Best thing to do is try a small scale experiment with it and see if it does what you want. Never know till you try it!!!

The fabric idea seems to revolve around fiberglass and resin. I've not the ability to handle breathing that stuff anymore-i've burned up my lungs in a former job. I seriously want to avoid fiberglass, and even lots of epoxy, if I can help it. Besides, I always sucked at working with fiberglass. Everything I've ever tried turned out "not very good".

[GPW]

Quote; “The fabric idea seems to revolve around fiberglass and resin.” ..... Not Really !!!

[pete42]

"Oh, almost forgot... NO BEER. We don't drink alcohol... Nor coffee. Nor soda."

beer grains and hops no meat there....................
I too don't drink alcohol did at one time just don't anymore my friends do and their still my friends.

[mdk]

Quote; “The fabric idea seems to revolve around fiberglass and resin.” ..... Not Really !!!

Ok, pardon my impertinence, but I have seen SOME talk of using epoxy (a two part resin) and cloth, rather than fiberglass and resin. I don't really see or understand the difference, other than some chemistry changes. But that aside, I don't know why you'd use cloth rather than wood? I haven't been able to find any good discussion on that ( I'm assuming it's out there, I just haven't found it), and I want the extra sturdiness of having a thin ply on both sides of the foam.

Where you don't need the strength, and if you like the finish, I can understand doing it (not saying fiberglass is weak, please don't misunderstand, but when very thin it tends to get a bit brittle) . A few years ago, I saw a lot of discussion about homebuilts and delaminating going on with the exterior... But I don't see that as an issue, since the foam is impregnable, as far as water goes, the lauan is nearly so, as well, and once you paint or coat it with something like a marine sealer or paint, it's all but totally impervious to water. Everything I could learn over the years about delamination was about moisture coming through from the back side (inside) or the edge and rotting the wood underneath whatever you used to coat it.

I'm still unsure of the strength of using 1/8 ply for the walls, as well. I'm not sure just where the strength is, in terms of load bearing and impact.

[mikeschn]

"Oh, almost forgot... NO BEER. We don't drink alcohol... Nor coffee. Nor soda."

beer grains and hops no meat there....................
I too don't drink alcohol did at one time just don't anymore my friends do and their still my friends.

Wow, if I could have as much discipline!

Mike...

[atahoekid]

Quote; “The fabric idea seems to revolve around fiberglass and resin.” ..... Not Really !!!

Ok, pardon my impertinence, but I have seen SOME talk of using epoxy (a two part resin) and cloth, rather than fiberglass and resin. I don't really see or understand the difference, other than some chemistry changes. But that aside, I don't know why you'd use cloth rather than wood? I haven't been able to find any good discussion on that ( I'm assuming it's out there, I just haven't found it), and I want the extra sturdiness of having a thin ply on both sides of the foam.

Where you don't need the strength, and if you like the finish, I can understand doing it (not saying fiberglass is weak, please don't misunderstand, but when very thin it tends to get a bit brittle) . A few years ago, I saw a lot of discussion about homebuilts and delaminating going on with the exterior... But I don't see that as an issue, since the foam is impregnable, as far as water goes, the lauan is nearly so, as well, and once you paint or coat it with something like a marine sealer or paint, it's all but totally impervious to water. Everything I could learn over the years about delamination was about moisture coming through from the back side (inside) or the edge and rotting the wood underneath whatever you used to coat it.

I'm still unsure of the strength of using 1/8 ply for the walls, as well. I'm not sure just where the strength is, in terms of load bearing and impact.

One of the things we've said on this forum is that you should build it the way you want it. If you want to use thicker wood, please don't think you're offending any of us. We have different needs and expectations of our trailers. For your interior skin you can use fiberglass and epoxy or canvas and TB2 or exterior enamel paint or some glue. It's certainly your choice.