Just a suggestion, I would put a big dab of silicone in the screw holes, then screw it down. Same in the front, rear, and top trim. What kind of finish are you going to use on the boards? Have you thought about the West System? It is expensive, but very hard, and durable, as it is used in the boating industry. Also it will seal the spaces, in between the boards. You could put a sheet of FG cloth on it, and brush on the West System, and it will be clear, and you can still see the wood, and the grain, etc. That thing is looking prettier and prettier, each photo session. Next project, redneck, Motor Coach!
Wayne