What I am suggesting, is that there be a series of sound abatement baffles in any opening. Imagine a tube, with one baffle coming up a little mote than halfway, then a little further along another baffle coming down the other way, all lined with absorbent material. This is fairly common so there should be diagrams readily available.
In the hotel
we used high density glass mat. In a boat I would be using the purpose made stuff which is silver on one side and sticky on the back for easy mounting. If you need more air an in line fan in some ducting will help. The crucial thing is no straight air gaps. This guy went around everything with the edge of a credit card, and if there was any gap it had to be sealed. His name is Louis Challis, and he has an Order of Australia
for his work in sound engineering and he really knew his work. Cost more than going to the dentist, though!!. Regards, Richard.