I am planning to build a skirt/ snow shovel protection base on part of my dome near my door ( using 6 ft. long X 3 ft. high x 3/8 in. thick treated plywood) and 6 inches of the plywood will be below grade in gravel near a plastic drainage tile. It may still get wet and snow will pile against it at times. I have read, in a boating forum, re getting the plywood dry before applying paint or preservative. What green alternatives do i have re paint or preservative for longest life??? I have to paint the outside facing side. Thanks.