there's lots of stuff that you can use to weather-proof outdoors, but just a good exterior paint would probably be the best thing for you to use. Nothing fancy, and not too expensive.
good luck, and as a cat-lover myself, thanks for having a kind heart!
any exterior enamel paint will work ,
if you have a big lots store near by they sell it cheaper,
brand names are just that, a Name, paint is made at a factory, and different labels are put on, the cans with the same paint in it,
