I can't believe I'm the 1st one to think of this... but if I am, here it is! There are a few problems with the hatch on the Spartan.
1) It doesn't seal simply by attaching it to the hull.
2) If it were to come off, it would sink.
3) It's ugly from the bottom.
Maybe you see where I'm headed with this... maybe not. I plan on sealing the underside of the hatch with a piece of plastic. Once that's done, I'll put weather stripping on the new piece of plastic so that it seals to the hull. By sealing the hatch with plastic, it will form an air pocket inside the hatch so that the hatch floats if it comes off. If I can't get the hatch water tight, I'll just fill it with expanding foam. Pics coming later tonight or tomorrow.
Well it didn't work quite like I had planned. It's darn near impossible to get the plastic to fit PERFECTLY on the very very tiny edge of that hatch. I ended up putting the plastic in on the inner lip.