If you do happen to burn the filler, you can always unpack the filler, clean and dry burn, and repack with the fresher side down.
OOOORrr you can leave the packing out and just drip.
If you keep one for dripping, you have backup filler for the others.
If you're punching these for tanks, make a small groove with a hack saw or something before punching so the shell doesn't crunch (like a pilot 'hole' of sorts). If it's not crunched it makes removing/replacing the filler easier.