The best solution is using an expanded PVC material or plexiglass and not wood. Plexiglass is too expensive. I think my next build will be out of expanded PVC.
If you are going with wood, the first thing that will help tremendously is to be sure you use a good exterior grade plywood. Totally different type of glue and will last much longer. As far as a coating - I have tried so many over the years!! The only one I will use now is Rustoleum Countertop Paint. I have had great resultsw with it and since it is food safe, I feel good about the safety. It is reasonably priced and much easier than a 2 part epoxy to work with. Good wood. A good primer. Then a few coats of the countertop paint. I have some enclosures now almost 3 years in use and absolutely no degradation to the coating at all.
I wanted to use expanded PVC but couldn't find it anywhere in town.
I end up using some rubber coating. It works pretty good except I have to put some thing on the corner walls BC he tryst to climb it and flip him self..
I purchased my expanded PVC at Home Depot.
Veranda 1/2 x 48 x 96 inch sheets of cellular white panel. Model HDSHSM124808. Price locally $67.48
Hope this is helpful!
I went to home depot and they said they didn't carry it and I looked around. I'll have to check again. Thanks