Hey Grigg if you want some thing like inner tube try butyl rubber pond liner in 100 mil it can be had in large flat sheets and any place that carries it will also have vulcanizing glue that will work for the seam. Where it joins the truck try Sashcos' Through the Roof it's a clear brushable silicone roof sealer. The interior will need to be upholstered to look good hit the outside with a coat of paint mite add some flex agent to the paint.
