Coating wire mesh (rat cage)?

I have no experience with rats, so here's my best guess. You might try some of that stuff that they dip tool handles in to make them electrically safe. Pliers and the like. It's available in hardware stores, usually in a can, about 15 oz. or so. It's a thick plastic liquid material that dries in maybe an hour or so. I'd be worried about the animal nibbling on whatever you use, but I think this stuff would be safe.