Going through the same thing myself and have decided.
- My batteries are going in the bilge.
- They will be AGM's
When my engine
starts, my blower (250cfm continuous duty)(actually sucking air) will start automatically (and/or manully and/or timer). It draws air from under the sole (which is sealed somewhat to the hull) and through the engine
room and out. There will be an opening towards the bow which allows air from the V-birth to under the sole area. In the pilothouse (high and toward the stern) incoming ventilation will mitigate negative pressure in the boat. This will setup circular air flow and help keep, the bilge
dry, boat dry and use the cooler, lower air to cool the engine room. The blower pushes the air out a vent on the starboard side stern of the boat.
Might not be perfect, but that's where I'm at.