I used minwax waterbased polyurethane, two coats for my wood frame cage, it's working very well so far at resisting water absorption. It's available at home depot and probably any other home improvement store, and while it's a little pricey, I really appreciated how little off-gassing of nasty fumes it had. I left it outdoors in the sun for about a week to make sure it was well cured before I started using it.