Charlie, mine is a sailing box too, and I had a similar water fountain through the dagger board trunk under power... I was able to seal it. I suspect there are some photos back in my build sequence a couple years ago.... but basically I built a full depth plug out of some soft Azek trim stock (I wanted to ensure that if there was any freezing, the plug would absorb the pressure and not put pressure on the trunk).....I then made a flange on the deck, gasket made of neoprene. I used 6 SS #12 x 3 inch wood screws... and to ensure I had not leak/rot issues. I core drilled the screw holes 3/4", filled with epoxy and cabosil. After cured, I re-drilled. No leaks now![/QUOTE]
Thanks for posting Dave, I have a plug in the deck where the daggerboard trunk is. Its made of cedar and wrapped in electrical tape. The water pressure pops it up a bit at times and water leaks onto the deck. I like your neoprene idea, Sounds like a good fix