Nice work BigD! I would recommend exterior grade latex paint over a couple of layers of exterior latex primer. It is easy to work with, easy to clean, and being exterior grade, it is very water resistant. Before you paint it, I would also recommend getting the paintable latex/silicone caulk and seal all of your edges, corners, and nail holes prior ro painting. That will help keep the wood from warping and the nails/screws from rusting and failing. BTW, using white semigloss for the interior of the hood is best since it will halp reflect as much light into the tank as possible.