I didn't have any fiberglass resin that was still good, but fiberglass might be the best answer. I had to make this piece (with clear epoxy) thicker than usual because of the heat problem, but even thin fiberglass tolerates heat very well. Here in Dallas the internal temp of a vehicle can exceed 150 F easily and I've even seen it reach 170 F...and I should add the thermometer I had stopped at 175 F as the high limit, so it could have been hotter I suppose. The main problem I had was bubbles in the clear epoxy.
