Less ventilation!
Which has minor consequences, such as more mould growing in the boat, but nothing more than that. We had those two on the 40 Ocean. In the deep of winter I would tape them both up. Even with the forced air diesel heater sucking its combustion air from this area, there was no issue - the companionway hatch was drafty enough to let new air in!
We ran a dehumidifier in the cabin to control the humidity though.