You cham wont eat the wood that the paint is on so dont worry about it. I used Helmans outdoor and weather proof sealer. Its in a green can and says UV proff, water proof, and weather proof or somethign like that. Let the cage air out for a few days after the last coat and use a diluted anti bacterial soap to wash it down and rinse it off well. This stuff works great and my cage is misted 7 times a day for 5 min at a time so it is pretty wet on the floor and the base during the day. I would put more coats at the bottom to help combat the mositure since that is where it will all collect at. Use about 3-4 coats and sand between for the bottom portions and about 2-3 coats for the rest. Have you seen pics of mine?
the last pic is of the floor which is actually fake tile that is silconed around the edges to seal it up and the bottom edge is what I was talking about. I just had to resand it slightly and add 2 more coats so that is why I am giveing oyu the heads up to add more coats the first time.