I had the same problem with my 1985 32' w/flybridge. I talked to Tom Slane, but he only had a leftover vent with a drain box from some other boat and it needed work. As we (my mechanic and I) saw it, we needed to have a drain box on the inside that would not allow water to come into the engine compartment, but drain out somehow and still let the air in.
As best as I understand, my mechanic designed a drain box made of quarter inch Starboard with a baffle in it. In the middle of the box, the baffle wall is attached to the bottom of the box to force the water to drain outside, and the top of the baffle has an opening so the air gets in without the water. It's really simple. On the inside top, he has a few 3-4" holes for the air to flow into the engine compartment with hoses attached to force the air down around the engines and a blower attached to one of them. It works great and since he installed them I have not had any water coming in.
If your interested, I could get a more specific and accurate design and write it up for you. Karl
