I hear mixed reviews on the foam, I always heard that Great Stuff is closed cell foam, and therefore should not collect water, then other people say it accelerates rot. I'd use it anyway, lol. My friend took beer boxes and made a form on the side of his 2 dr Tahoe where the lower quarter rotted, sprayed foam in there, then trimmed it to be more accurate with the body lines, fiberglassed it, then painted it!