I sealed the top skin as I riveted it, made sealed 'cups' around the hinges forward of the sub-panel so that no water can get forward of that panel. Then I covered all the instruments with a thick clear plastic and 3M 471 tape fwd, and velcro aft to keep the remaining water off of anything important yet still be able to get in there. I will typically see a touch of water on the plastic after a flight near the hinges only, but it is easily tacked up with a towel.
