What to use for plugging access holes...

[LBJ]

in the door panels? When I removed the plastic door trim panels, there was some tar-paper-like material covering the access holes on the steel door panel. The stuff was WAY old and I'd like to put something there before I replace the plastic trim panels. Any suggestions? I thought of using some sound deadener material, but that's about all I've come up with. I think it should be one piece so it doesn't come apart over time and held on with some contact cement. But, what will hold up over the years? LBJ