In the aft section of my 16' plywood skiff that I am close to completing, there are two epoxied and taped flotation compartments that I built. They are about 24" wide and I filled them with the blue foam insullation board from Lowes. I recently took the boat to the shop to have the steering and motor installed. They screwed a clamp to the .25" plywood cover on the flotation compartment to attach the throttle cables, penetrating the cover. I of course didn't like the location of the clamp, so I removed the screw and clamp. As I removed the screw, I heard "Pssssss", air either entering or escaping through the screw hole. Air is obviously trapped inside the compartment and expanding and contracting with the weather/temp. Everything is epoxied and taped, so it is air tight. Should there be some type of ventilation for the compartment? Or is it better sealed up. I could drill a hole where it would not be exposed to rain water, but then water could enter if I swamped, also, would ambient moisture be more likely to accumulate in the compartment. What I don't want is moisture to accumulate in the bottom of the compartment, leading to problems down the road. What do you all think, seal up or vent?