Something else to consider. The battery compartment is right next to the engine and also needs to be vented when the batteries are charging. I have a vent between the engine and the battery compartment. There is also a vent into the hanging locker (which has been converted into drawers). When the engine is running the blower is on, sucking air from inside the boat through the hanging locker, the battery compartment and into the engine compartment. I am working on a smaller fan that will do the same when plugged into shore power with the battery charger
Oh, and the Volvo is out of the engine compartment and the engine beds removed. Would you believe the beds are screwed together 3" x 8" solid mahogany (total 6" wide), bedded to the hull in epoxy
and glassed into the engine compartment hull only. On the bulkhead sides (galley and quarterberth) they were only stapled, no glue anywhere! There was a rattle at cruising RPM that I couldn't locate. Now I know where it came from!