Sealing this leaky hatch

[oldfielder]

Hey guys-
I'm trying to sea up what I guess used to be the livewell hatch on my 23. It has no lip and I suspect it lets most of the freshwater into the bilge, as that's where the well drains. I'm assuming some kind of gasket won't be enough. Do I need to get some kind of gemlux latch to replace the pull?
Any advice appreciated.

oF