Hi ya there Kenny - food for thought
Is it possible to create an inner flange out of either plywood or thick plasticard on the inside of your aftdeck hatch?
Ive posted a couple of pics of how I overcame the problem on the Seaforth Conqueror when I built her. I used the elastic bands what we get from the postie when he delivers letters to form a seal. I create a thick flange out of 1/4" timber on the hatch lid to press down on the elastic bands. Then as you can see, Ive used brass screws - some days I will have to paint these and camouflage these in.
What I did to test it, I laid toilet tissue inside the hull, screwed the back deck down and then put it in the old test tank THE BATH and submerged the rear end OF THE MODEL
for a few minutes. I then removed the model from the bath and then removed the hatch - I then looked for seapage on the tissue paper. There wasnt a great deal, very little in fact.
Its worth a try though.
With it being screwed down, the hatch only takes a couple of minutes to unscrew. Hope this is of some help.
aye
John E
Bluebird