I'm just spitballing here. I'm trying to keep weight to a minimum in my truck bed camper and am considering making the cabinets and bed platform with foam.
I know xps has great compression strength, but what about when it's vertical? If it's standing on edge, would it support a bed platform? Maybe make a frame with vertical supports using wood and 1" foam to fill it in, then PMF the whole thing using bed sheets or something light-weight. The foam would then be 1" thick and lighter than 3/4" ply.
Also, what about the platform? Do you think a 30" wide 1" xps with PMF would be okay for a sleeping platform? Maybe 1/8" luan on both sides and then PMF? Or, a few 1x4 supports? Maybe by the time I do all that, I've done a lot more work to save very little weight.
I can't seem to find anyone who has experience using foam this way.