I haven't seen one in person(still looking to buy one) but from the pics I've seen, if it were me, I'd frame it all in with 1/2" aluminum angle for support and spray it with polyurethane foam. then use the angle aluminum is supports to screw coverings on.
insulation is one of my biggest concerns when buying an RV. what are your walls like? are there any or a lot of empty voids in the walls and floor?
I really want a close look at a BT cruiser but there are none in my area, sadly.