Just some thoughts for you when you're clamping drum shells:
You can use pieces of wood running the length of your drum shell - one outside and another inside the shell. If the wood has a very slight concave attitude this will help put pressure on the shell when you clamp it (kind of like a spring). But it can be just two straight pieces of wood - it will work fine.
I used this method to clamp & reglue wrap on some drums. I know your task is different but the method should work in your case as well.
The above method is just a handy way to clamp if you don't have clamps that will span the length of your drum shell.