[E-Type] Gas sump sealer, donut thingy

I had a gas leak at the sump of my 67 FHC. The old sealing ring was crumbled rubbery stuff, so I went to eagle hardware and found a rubber gasket that fits well. Should this sealing ring be rubber? Will the gas deteriorate it? Also, the under tank pad thingy is missing, allowing exhaust fumes to come up through the sump opening and into the car. Can this be replaced without removing the tank? Thanks!

Norm Black
67 FHC
63 OTS
Seattle, Wash.