What I would use (and have used) for axles and wheels is appliance epoxy paint. Rustoleum makes a good one, takes a couple days to cure completely, but when it's done you can practically hit it with a hammer. And, its only a few bucks a can.
Brad (from the 4 Wheeling center of the universe, 4 corners USA)
Brad (from the 4 Wheeling center of the universe, 4 corners USA)