Earlier, Bill Daniels wrote:

...Gary Sutherland's MOBA...

Exactly! That's been a feature of all of my back-of-the-envelope
sketches for pressurized sailplanes, ever since I saw the MOBA in one
of Stan Hall's articles. The circular opening keeps the seal perimeter
to a minimum, and it would be very easy to seal using a conventional or
inflatable sealing ring. And you could even use a simple eighth-turn
thread to latch it with very few moving parts.

However, one major issue with that arrangement is emergency egress.
That's got pyrotechnics written all over it...

Thanks, Bob K.