How to fuelproof?
Mix up some epoxy, add a few drops of plain ol' rubbing alcohol until it's thin, and pour it in, or brush it on. The epoxy will take a lot longer to cure than normal (Like 24 - 48 hrs). Keeping it in a warm place will speed it up. Works like a charm.
Some people will tell you that you ned to use a special kind of alcohol, this may be true if you are thinning the epoxy for structural use, but for fuel-proofing, any kind will do.