Any kind of two part epoxy resin--like the stuff they use for tables and
wood clocks will waterproof coat just about anything. You can get equal
part mixed stuff at some hardwares and craft stores. I'm lucky enough to
live where they make surfboards, so we have a local supplier to get all
kinds of resin. I have done it on papier mache' with great results. It is
a bit squirrley to work with and definitely messy, but it will do the trick.
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