I've just built an 8' steam box to help my daughter's classroom build a toboggan. It is 1/2" plywood with 2" EPS form for insulation and then another 1/2" plywood layer. Can I use my leftover epoxy to seal it up so it doesn't absorb water and weigh a ton, or will the epoxy go soft when the heat inside the box gets to 212 F? Should I glass the inside. I have extra glass pieces from the many boats I've built. Thanks. BTW- I have a leftover Raka 127 resin and 350 harderner.