we get 40"+ rain a year, Ive been using this "utility board" for a while now for lids and inner covers. Of course all of it is either covered in aluminum flashing or edges inside pine frame. It used to be luan that they sold at lowes, not it says "hardwood utility panel". These will be painted with exterior latex two coats. Ive also thought about using epoxy resin to paint the outsides as I used to do that with mdf and other enclosures to water proof them. When you put the resin on, it soaks into the wood a few mm. I think the exterior latex is fine though. If they last a season at 3.00 (including glue, paint, and staples), Im happy with that. Ill put a foam seal around the plywood lids which screw down into the frame. I still need to add the hangers.