Here's a possibility for hinges:
https://www.mcmaster.com/#piano-hinges/=1837el7
I've also used aluminum hinges in the boats since they are a lot cheaper. Another possibility might be to have the tanks above the hatch an inch or so, so the hatch could slide open from under the tanks. You could use a piece of starboard, trex, or wood to support the bottom of the tanks with enough clearance to slide the hatch out from under the tanks. Not sure if it would work with your configuration, but worth a look.