Hatch gasket?

[390Express]

My boat has a large hatch that opens with two hydraulic rams, and a smaller hatch in the large hatch for quick access, and in case I need access with dead batteries. I had water in the motors when I bought it, and knew about it and drained it all out. Water got in the port motor a 2nd time after I bought it, and I think it came through the engine compartment. I was worried that it was a head gasket or worse, but I did notice after cleaning that I had sudsy water all over my motors, and I didn't use a hard spray. I'm guessing its leaking through the small access hatch hole. I did check and the channel is free and clear, and the drains are open. It used to have a foam gasket mounted on the top piece of the hatch, and it's pretty well shot. I'm guessing it needs replacing. Is this what I need, and if so, what width and thickness is best? My old one is too shot to get dimensions from. Also, when installing, how best to handle the corners? I’m guessing butt joints, should I use some sealer at the joints too, or just keep it tight? It’s on of those deals where I’m guessing overlap will cause a bad seal.

[390Express]

I bought the Taco 3/4” wide by 1/8 thick gasket and it worked great.

Before and after:

[390Express]

The small gaps near the back of the gasket are intentional. There isn’t anything critical there, so if it’s going to get overwhelmed and spill, I figured I’d like to be able to control it as much as possible, and create the area it would do it at.

Also sanded with 220 on an orbital sander, and painted with rustoleum pure white. Looks good and it’s been extremely durable.