I do understand the concern about drainage. Being a taildragger, I don't think drainage would be an issue. I am only thinking about the 6 lower wing access panels, particularly the 2 that are C/T the pitot controller and AP servo.
Ricks method is what we did at the airlines, I wonder if instead of proseal, what about a very thin layer of clear RTV, let cure then put the panels on.
I am concerned about this as on our way back from SNF this year, my friends TruTrak servos got waterlogged and froze at altitude. We were on short final in terribly gusty conditions when the servo finally sheared and it made for quite a ride 20 feet off the ground. Apparently TT said this had never happened before? I suppose the tornado/ horizontal rain may have had something to do with it.