Keep an eye on that thru hull if it's original. They were threaded plastic from the factory. Easily cracked due too stress between the inner liner & outer hull allowing water intrusion to the bilge... No Insulation between liner & hull, upper nor under. I replaced mine with S/S Gem make utilizing a drain plug inside.

I’ve always used that hatch as a fish box. A long time ago,I used styrofoam under the lid for the times when we would be gone for a few days. I’d load ice blocks in and after a long trailer ride, no ice melted. I have a bronze drain and I did notice that once in the warm water, the ice would not last as well. Part of that I attribute to the drain in contact with the water. To let water out of the drain, I would have to reach in and pull the plug, then go back to the stern, then go quickly back to put the plug back in. I don’t understand how no water comes in your hatch. If I don’t have a plug in, I get water in even underway with waves and all.