I just used a good exterior grade primer, 2 coats. And 3 coats exterior paint on the bottom of the floor. Epoxied the bottom of the walls. PL'd the walls to the side of the floor sandwiching the verticle leg of the frame angle iron. It is sealed nicely. I used up any varnish I had in the house on the exterior. Thinned 50%, then 25% for the last couple coats. Covered with aluminum skins. Maybe overkill? But what ever it takes!!