If you're going to use a hatch with no latches and a positive seal, you'll need to vent the bulkheads to prevent pressure buildup on warm days. Can you imagine paddling along on a sunny day and suddenly POOM!, your hatch cover blows off? ;-)

All it takes is a tiny hole. On the foam bulkheads of my plastic boat, I installed pieces of plastic aerosol spray can tubing (the skinny red tubes that come with WD-40 and other sprays). They provide plenty of airflow, but the hole is too small to pass any significant amount of water, especially considering that the compartments are otherwise air tight.