Hi, Joe!
I wonder if you meant to ask your question on our sister-site, the
Forest River Forums.
It's true there may be a few people here with some knowledge of rubber roofing material, but as Frederick explained, we're all about fiberglass trailers that are constructed using molds (usually 2 pieces, sometimes 3 or 4).
For those who don't know, the family of websites that FiberglassRV.com joined a couple of years ago includes one dedicated to the Forest River RV brand!