Well I see a few weak points in where you're headed with this. I would tell you to scrap the whole train of thought there. Since you have not made the hatch yet it's not too late.
Reason I say that is water is such sneaky stuff. It won't take much to sneak past that seal the way it's set up now. Wind driven rain, slight misalignment of hatch to seal, etc. Once it's past the seal your doomed. You will get water in that spiffy galley you built. In your mock up that 45 degree wall cut will actually help the water into the galley.
I think you could modify your hatch and walls to use Steve Fredricks hatch seal method. Or a modified version of it.
See this thread for some great pictures of his system:
http://tnttt.com/viewtopic.php?f=21&t=61506If you look at the first pic in that thread, I think you should mull over a way to make that raised lip on the inside edge of the galley wall. That way the water can't get in because it's blocked by that wall. It has no choice but to run down the dam wall and out the bottom. You could add a curved piece to your wall to follow the profile to create the water dam. Better yet as thick as your wall is, maybe router into the wall from the outside surface, but leave enough of the inside galley surface to create the water dam as you see in that thread.
The way the system works it the weatherstrip would seal on top of that water dam wall. The seal goes up in the hatch.
Even if you still sealed it at the outer edge, you would be way better off with that water dam wall in your seal design.
Maybe look at it from a whole fresh direction?
Kick it around. Post back some thoughts. Good luck with it.