Hi all, sometime lurker, new poster

[mdk]

I've been reading the forums with great interest for a little while now, and i'm interested in building my own TT. But not a teardrop. For some reason, I can find little else but this site for build it yourself RV trailers.

Then again, you guys are inventive, and I want to be inventive.

My ultimate goal, if I can manage it, would be to build a travel trailer about 20 foot long, and under 2000 lbs sprung weight. That's fully self contained, including heat, a/c, fully made up queen size bed, etc.

I've gotten somewhat inspired by some articles here, and started work on figuring out some construction techniques that would possibly work.

I decided on building walls made up of 2 inch EPS foam, glued to 1/8 ply inside and out, and some carefully designed stiffeners made of 1/4 and 1/8 ply on 16 in centers. Roof design matches.

I designed an aluminum frame, with very careful attention to spreading the load, using rectangular tubing, and ended up under 150 lbs weight for the frame sans springs, axle, brakes, and tires. It would be made of 2x2 and 2x4 rectangle, full perimeter frame, with the axle load spread across quite a bit of it, lengthwise. it would seem be strong enough to me.

Sadly, I have no way of showing the details here, as I simply cannot fathom how you operate any of the CAD programs.

This trailer would have a 6-6 ceiling height, a little under 8 foot wide. Would have the last 5 feet sloped down a 4.5 foot back wall height, and the front 2 feet sloped at 45 degrees. Also, there appears to be a possibilty to extend the nose not far from the jack, so that the front is a sloping, blunt nose V, to hide the propane.

I'm currently debating 2 or 3 inch thick walls, which would be 10 to 15 R Value. The walls would be constructed with a hollow 1.25 X 2 or 3 in box ( foam filled) as vertical studs, with 1/8 in ply bonded to the foam and to the box studs and to a bonded multi layer sill plate made of 1/4 ply both top and bottom. These hollow vertical studs give the ability to screw to the floor and to the edges and top, through many layered plywood. The walls would resemble SIP's, with light wood bonded to a thick layer of relatively squish resistant foam.

I was going to just hang the tanks from the frame in the open, but now I'm letting my imagination run and seeing if I can actually enclose the whole bottom, and keep my tanks inside the insulated area for cold weather camping... And still stay light...

I'm at a loss for ideas for bellypan material that's light, strong, doesn't leak, air or water, and not terribly expensive. "light strong cheap" doesn't normally exist... you get your choice of any two...

I've even come up with plans that use 1/4 in plywood for the floor, ing supported with a sort of manufactured honeycomb of vertical members filled with high density foam. But that one has made me rather nervous, since much of the wall's stiffness comes from having flat sheets solidly attached to the floor, wall, and ceiling, to provide box type reinforcement.

I would even try a triangular reinforced ladder type frame that was 8 inches deep or so, if I could figure out how it could be done super light, and enclose the whole floor and tanks and insulation within it. Sadly, my imagination isn't good enough to fill the bill on that one.

I have even mulled over a number of ideas that involve minimal trailer frame, involving just a shortened aluminum subframe and tongue, and the trailer itself is the structure. But, pound for pound, aluminum seems to be stronger, so I think that idea is self defeating.

Any great, not so great, bad, or off the wall ideas appreciated.

You can even tell me i'm nuts... That's ok, just as long as i get some added fuel for the imagination...

[madjack]

Md, you certainly have some ambitious plans...have you looked at or considered a cargo trailer conversion...keep in mind that the volume of area you are wanting enclose is still small and as such, it is not going to be hard to heat/cool...a 1 or 1-1/2" thick wall would probably be sufficient...tanks...using pvc/abs piping built into the floor or even a custom built tank to fit in the floor may be a better way to go...custom built tanks are not cheap but are not prohibitive either (here is one of many such places http://www.plastic-mart.com/ ... http://www.watertanks.com/ is another)...if you have a scanner, you can draw up plans, scan them, save them as .jpg files and follow the "Help with Photos" link in the top index to post them here...good luck and have fun.....
madjack

p.s. oh yeah...welcome, I'm glad we could get your activation problems ironed out.......MJ

[mikeschn]

Hi MD,

Welcome to the forum. MJ is right, that is quite an ambitious project you got going there, with a lofty lightweight goal. My 10' trailer was 1500# so a 20' trailer should be 3000#. Well okay, not exactly, you're building lighter than I did.

If you have your plans drawn out on paper, you can also take a picture of them, and upload them to your album.

Have fun, and keep posting the details!

Mike...

[angib]

This sounds fascinating and I hope we'll see more of this project. A few thoughts or comments for you:

I'm with Jack on the skin thicknesses - 2" sounds plenty for strength reasons on both the walls and roof.

If you are planning to put 1/8 or 1/4 ply webs inside the sandwiches and you can make an effective bond between the end of the web and the skin panels, then your walls and roof will be hugely strong overall (though perhaps at risk of being punctured by sharp objects).

I'm uncertain about your joints at the bottom of the walls - are you planning a single layer of 1/4" ply as a sole plate? If so, the strength of the joint would depend entirely on how well the sole was glued to the skins. Using epoxy I can see it working, but not with anything less. Clearly the bond to the foam isn't important here as the foam will break at a low load, so it's the joint to the skins that matters.

For the floor, you could use exactly the same technique as the walls, except with the webs spaced a little closer together than 16". It is not an advantage to run these webs in two directions (a very common structural misconception) as long as you run the single direction across the other supports - most likely this would be transverse floor webs picking up several longitudinal frame members.

For the main rails, 2x4 aluminium rectangle tube isn't super-strong - it's only a little stronger than a 2x2x1/8 steel tube, but I think that would be enough for a 60" long tongue on a 2000lb trailer. I'm assuming you're planning an A-frame tongue - a single 2x4 Al tube tongue would undoubtedly too weak. 2x2 square tube for the rest of the frame sounds just right.

Andrew

[angib]

My 10' trailer was 1500# so a 20' trailer should be 3000#.

As you would expect the weight of the trailer to go up at least as much as the surface area goes up (his 20' trailer is twice as high and twice as wide as your 10' trailer), you would expect the 20' trailer to be at least 4 times (2 squared) as heavy and probably more....

Andrew

[mdk]

I'm uncertain about your joints at the bottom of the walls - are you planning a single layer of 1/4" ply as a sole plate? If so, the strength of the joint would depend entirely on how well the sole was glued to the skins. Using epoxy I can see it working, but not with anything less. Clearly the bond to the foam isn't important here as the foam will break at a low load, so it's the joint to the skins that matters.

No, after some thought, I decided against the 3/4 plywood I was going to use, and decided that 1/4 ply, built up (glued and screwed) in 2 or 3 layers, so that the joints are far from each other would be strongest - or at least not have any single weak spots.

And yes, the idea is to use the strongest, most durable glues I can find. Gorilla Glue is one... impervious to humidity, too.

For the floor, you could use exactly the same technique as the walls, except with the webs spaced a little closer together than 16". It is not an advantage to run these webs in two directions (a very common structural misconception) as long as you run the single direction across the other supports - most likely this would be transverse floor webs picking up several longitudinal frame members.

I did not know that. However, this floor will be stressed in three directions... First being holding up weight, second being fore-aft forces and third being side to side forces. So, it has to have at least SOME bracing in in both axes to prevent the top from wanting to move relative to the bottom. I don't want to rely solely on the edge of the "box" for that strength, I'd like to spread the load around a bit.

For the main rails, 2x4 aluminium rectangle tube isn't super-strong - it's only a little stronger than a 2x2x1/8 steel tube, but I think that would be enough for a 60" long tongue on a 2000lb trailer. I'm assuming you're planning an A-frame tongue - a single 2x4 Al tube tongue would undoubtedly too weak. 2x2 square tube for the rest of the frame sounds just right.

Andrew

What I had in mind was 3 2x2 tubes for the a-frame tongue of about 5 foot from the end of the frame, with the tubes going back behind at least 2 cross members.

This idea is a perimeter frame that goes OUTSIDE the tires, with cross members and the 2x2 tongue center extending all the way to the back.

then, the axle springs mount to 2x4 or larger (if I need the space for the tanks) subframe members that spread the weight across at least 4 crossmembers. These crossmembers will be closer in the middle, and the plan is to put the tanks slightly forward of centered on the axle. Even the fresh water tank under the floor slung above the axle.

This might mean having the trailer a little high off the ground, but since it may see uneven terrain, that's not a bad idea.

Thus, the center of the frame has a vagulely double H appearing outline.

I'm working on seeing if I can master sketchup... Maybe that'll be easier. It looks easier. I'm no artist. I can fix your computer, your cars, your appliances and most anything else, but I can't draw for spit...

One last note, I struggled for a long time thinking I'd like Filon on the outside, but eventually decided against it. It's heavy, requires a lot of glue and backing and care to install, not to mention, gawdawful expensive, and am currently looking at a polyurethane or epoxy solid filled paint. Both of which are somewhat similar to your garage floor paint, but both penetrate wood well, and the ones I researched are bulletproof water resistant.

Among other notions, I also decided that the joints at the corners, roof, etc, all need to be fiberglassed. So, all the outside corners will be fiberglassed, then painted over.

Haven't chosen a paint scheme yet, but likely white, gray, and silver.