I spent the day stripping down a 1988 Coleman Sequoia popup. It had serious water issues but has a very good frame under it. Having already removed the dinette, galley, and cabinets, today was all about the top and outside. So silly me figured that between my son & I we should be able to lift off the roof. It's just white foam insulate with cheap paneling laminated to it. And most of the paneling was gone because of the water. Um, yeah, right! We nearly dropped it initially and really just chucked it over the side. It made no sense to me why the roof was so heavy. Until we started breaking it down. The white foam insulation that is the core of that style, between the aluminum skin exterior and the paneling interior, had become a sponge. It was literally dripping with water. I never saw that type of styrofoam suck up water like that. And the weight difference was absolutely unreal! Nevermind the obvious mold that had grown in the formerly white foam.
So - based on my experience today - I will NOT be using that same white foam insulation. It's blue board for me. Hopefully I'll never have my own water issues. But at least if I do, the problem won't be amplified by a sponge sucking it up!