I've got most of my paper build finished and I'm looking to harden, I saw that "epoxy resin" works well. I bought this epoxy at the hardware store and when I applied it to the shoulder it made it a bit tougher after two coats but its a bit floppy, it's turning it into kind of a rubber instead of plastic, is this not the right type? I don't think I can sand this slightly sticky surface, do I bondo over it? fiberglass the inside? Thanks for the help.