Hi Jumper.
These are some of the mods I have made which improve it a lot, for you perusal
Definitely ditch the gasket, not enough surface area to make an effective seal, my seal is about 1 Inch wide on each side of the hole nice and big no leaks.
I also placed some extra bolts in on the corners to give the hatch a better more uniform " pull down ".
Also ditch the Ali plate and use it as a template for some 1/4 thick Lexan so you can see into the inside to see everthing working and check for water ingress etc.
My Engle Akula's access hole is ok for size as I can remove the tanks etc ok, try a dummy run first with all the components in place and the middle deck held in place with tape and see if you can get the tanks out again.
A couple of pics of mine for you.
Hope its of use Sub.