by KCStudly » Thu Jul 02, 2015 11:38 am
From studying those links, what is not resolved is getting a large sheet to form to a specific profile. Most of his examples are free form, or he coaxes a smaller shape by hand into the approximate shape. I suspect that it looks easier than it is because he just puts a tension strap between the ends of a tight bend. You can't always do that on a camper and shallow bends don't apply much sideways force toward the glue surface. In other words the strap does a fine job approximating a profile curve, but does a lousy job clamping said curve to a mating surface.
Another option (that GPW has recommended) would be to laminate chip board or bed sheet to the outside of the foam before forming, then it would act like the compression strap while forming and prevent the outer surface of the foam from cracking/snapping. I haven't tried that method so I can't say how much harder it would make the foam to bend and stay put while gluing.
From my experience using a simple stretcher (technically not a compression strap because it did not contain the ends of the foam) it is very difficult to get the foam to form and press up to the mating surface(s) for a good glue joint. If any part of the profile is relatively flat, the stretcher or strap is not going to pull sideways over the flatter areas to affect a clamp. When laminating curved panels with kerfs, and especially using contact adhesive, large panels formed easily and stuck fast with just hand pressure.
The big issue I see if you want to try to form over a mold, is that you either have to spend time and materials building the mold, or temporary supports in the cabin to use it as a mold. My logic was that if I was going spend money and effort on building something to do that, why not make it part of the camper to begin with? But then I am not being uber weight conscious in my build.
For doors and windows I'm in the camp that likes a wood frame (preferably cedar). One option would be to form the panel first, then, once it is stable, cut out for the window and glue in a frame. You may have to deal with some fairing issues if the foam and wood profiles don't match up well (or maybe if the foam is flexible enough it can be clamped to comply with the window frame at glue up), and your cuts would have to be pretty accurate for a snug fit.
Do you plan on having it be a curved window or let in flat?
KC
My Build:
The Poet Creek Express Hybrid Foamie
Poet Creek Or Bust
Engineering the TLAR way - "That Looks About Right"
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