I have a fuel computer on my boat with an alarm set to go off at the 20 gallon mark.
When the alarm goes off, I fill the tank and add StaBil, Star*Tron, and Ringfree at the 1oz per 10 gallons of fuel rate.
Never had an issue with moisture, Ethanol, or any other fuel related issues.
My typical fishing areas are within a 1 hour run to the furthest point I typically go, so I really don't burn a lot of fuel like the offshore guys do.
As for that deck hatch... Look at the underside of the hatch and get the brand and model number from it.
Those o-ring seals are replaceable.
If you do replace them, coat the new o-ring with a teflon gel of the type used on zippers and snaps and it should seal just fine.