: With no way for the air inside your boat to get in and out, the pressure
: could conceivably build up enough to damage the boat (split a seam?)
: Couldn't it? Someone will surely know if this is a legitimate concern.

Yes, this is a very real concern. The compartments in a wood boat are rigid and can be damamged by air temp/pressure changes if they're not vented in some manner. I would vote for hatches, for utility reasons, but deckplates on the bulhkeads will work. I would suggest putting small (~1/32") breather holes in the bulkhead, regardless. I've done this with every boat I've owned. It prevents pressure problems and has never caused any leakage.