Sno-Seal from a military surplus store. Gorilla Surplus on Broadway carries it - at least they do online.
Here's a link to an album of what CDBs look like with Sno-Seal (not my pics)
Be wary, though. The crepe soles that CDBs use soak water up so they aren't the best to use in wet conditions - your socks will still get wet.
No idea what to do about salt damage.