Just a couple ideas to throw out

[Gator417]

So these aren't just for foamies, but I figured I'd drop them here anyway.
1) Use an existing plastic or fg lid or covering, filled with foam (spray foam), for a hatch or door. There are golf carts where I work and I keep looking at the "roofs" on them (~3'×5') wondering if one could fill them with foam for rigidity and use them for a small pop-up roof or a covering for solar panels etc. Also, same theory, a lid from a plastic trash can for the same purpose. Getting bigger, a lid for a big dumpster (about 5'-6' square) with the same treatment. They even have provisions for hinging.
Be honest with me. Does this idea stink?
2)Use the top forward section of a 5th wheel for a small camper. I see them on Cl sometimes for free or real cheap. I can't help but visualize what it would look like to cut the bottom off and set the rest of it on a 12'-16' trailer (trim the back end off to fit, of course). Not sure about the old ones, but the new ones have a single piece of fg (or plastic) for the nose. Very aerodynamic and professional looking.
3)Could one use a small dehumidifier for an ac unit in a td? Thats what ac was originally designed to do & I think the smaller size would be just right for a td.
4)Would it be feasible to use some aluminum channel of various shapes (H, F, W etc) for joining walls to floor or ceiling to walls or floor to trailer etc? It might be cost prohibitive, but just wondering.
I think that's all for now, but I'm sure I forgot a couple. Please let me know if they've been tried or if they are unworkable ideas.
Gator

[Gator417]

I remember another idea/question. Would 4 pieces of 1/2" foam glued together be stronger than 1 piece of 2" foam?
I know this holds true for other materials, but not sure if it would be true for foam.
Gator

[KCStudly]

Last question first, laminating foam is more effort than it is worth. You have to fit twice as many pieces, and do twice as many glue ups. For curved profiles, with a good table saw setup kerfing is far easier and less effort to get the foam to bend than doing layers.

On swapping formed shells from other applications, there have been a couple of builds that used PU truck bed toppers as a starting point and at least one guy who re-purposed the FG roof cap off of a conversion van.

[JaggedEdges]

3) Dehumidifiers...

Welllll, you'd have to completely dismantle it and add fans and ducting in the right places. Close off the cold side and force air through it. I think they have a straight air path so they suck air straight past the expansion coil where water drops out then push it straight to the condenser coil which heats it back up again.

Since they blow their cold air back to the condenser as far as I know, this means that should you separate the airflow, the condenser might be undersized to cool much with ambient air. You miiiiight be able to mitigate this by having high speed fans, but that'll be like sleeping next to a jet engine.

Another problem is that if you want a cheap one to screw around with... used ones usually come broken in my experience.

A lot of people here will tell you that you don't want a small unit, but they were probably also the people telling you you didn't need to bother building with insulation unless you lived in Alaska. Also "Don't bother insulating the floor, the mattress is the insulation." Then in another post "You need more than 5000BTU because unlike a house TDs lose heat through floor...." ... yyyyeaaaahhhh....

If you've got the HVAC skills to do things like put in larger condensers etc, and custom plumb it to sit on your roof with the evap in a neat cabinet inside.... then I guess you wouldn't be messing around with dehumidifiers and would have rigged something custom already.

If I ever get bored enough some time, I might do something like pull the complete AC components out of an Aveo or other small econobox, then make a "hybrid" savonius rotor vertical axis wind turbine motor/genny on a clutch that can drive the AC direct mechanically, charge the battery, or have the motor/genny drive the AC.

[wagondude]

Last question first, laminating foam is more effort than it is worth. You have to fit twice as many pieces, and do twice as many glue ups. For curved profiles, with a good table saw setup kerfing is far easier and less effort to get the foam to bend than doing layers.

On swapping formed shells from other applications, there have been a couple of builds that used PU truck bed toppers as a starting point and at least one guy who re-purposed the FG roof cap off of a conversion van.

Plus the foam has no real grain, so unlike plywood, no real strength to be gained.

[linuxmanxxx]

If you laminate it with very thin Luan and glue it completely it gets crazy strong and light. Put minimal framing in between the foam with wood glue on it and glue the foam with a poly based glue or the 3M water based contact cement it will hold body weight standing. Did I say it's light? 4x8 with aluminum skin glued to outer Luan with heavy manufactured door was 480 including the metal trailer.

Sent from my Nexus 6P using Tapatalk

[QueticoBill]

I had dinner with a fellow that was designing stressed skin panels - foam core originally then honeycomb later - in 1980s and mentioned that instead of the mechanical roughening they used acetone in a spray bottle to give the foam some tooth for glueing to a hard skin.

[KCStudly]

Acetone turns polystyrene foam into a gooey mess. Maybe with a fine even mist you could put on just enough to create texture, but drip, sputters, or just plain too much will only ruin the surface and create huge (relatively speaking) divots for glue to fill.

Not for me.

[JaggedEdges]

Yeah, you'd want to be careful with that for sure, don't do it horizontal if it's going to drip, vertical, or tilted slightly toward you. Also, super good ventilation, or you're either going to pass out or blow yourself up with the acetone fumes.

However, the odd small divot isn't terrible, shouldn't compromise structural integrity noticeably if you get a handful per 8x4, and thermal insulation wise, I think 5/8" is the critical dimension, you get convection currents larger than that, and then a cold spot, in use as insulation the foam is there to stop the air moving around, which is really most of the insulation, so smaller than 5/8" holes/gaps and it's working for that.

[QueticoBill]

I'm sure the company that used the acetone in production for several years had some messes early on, but I am sure it worked over the years or they would have found another way. As far as insulation, Swedish research I read years ago shows 3/16" is enough for thermosiphon in walls, but I don't think that is a factor in a tear. I suspect a divot half way through leads to less loss than the conductivity of a spar or framing piece. And the foam certainly doesn't need to be continuous for strength as all it does is keep the skins separated and from buckling, and the skins do the work.

[JaggedEdges]

I've seen various numbers, but 5/8" is what google would show me today...



I phrase it like that, because it's becoming progressively more useless for specific/detailed searches... you be like "air gap" in the quotes, which are supposed to force exact term, it be like "Gap clothing on sale." "Nike air jordans 30% off", "Cheap air fares."

[QueticoBill]

The more esoteric subjects are definitely harder to google. The study I recall was for walls and the effects of gaps between insulation and the framing or sheathing, not double glass windows, and had to do with convective loops.