Jim, do you think if I covered the whole board in roof cement or tar, before attaching the metal, it would keep the moisture out? I have not attached it yet, because I still don't know what material would work best for the bond between galvanized metal and wood. Maybe even letting a sealant cure before attaching, like a rubber o-ring, of sorts. If that makes sense.
I am modifying this post, because I had a new plan.
I can just slip the metal cover on when used as a cover. That will allow it to remain dry when used as a bottom, plus an added bonus, the metal should cover the entrance holes.