Jim,

That's actually why I recommend a good sized fire, rather than propane torch. The bonfire approach roasts that rubber so fast that it literally squirts right out in a matter of seconds. Less heat buildup that way than an hour with a torch (just my theory).

Oh, and for final cleaning I stuck a wire brush-cup on the end of a drill and ran that through. Most common size is the right one, fits right in nice and snug. Leaves you with clean and shiney metal to work with.