Haven't posted to this in a while.
Haven't had a huge amount of time for building lately, but have managed to machine a small 39mm I/D bayonet ring for the hull. This was turned from billet stock, and is machined to accept a small 1.5mm thick o-ring to minimise the room required for the seal and maximise access.
Easy job on a lathe pretty much hopeless if you haven't. Aluminium is chosen as it's easy to maintain tight tolerance, and also retains reasonable rigidity on a small thickness, which you just wouldn't achieve with plastic.
The ring is shown dry fitted to the hull, and will be bonded in with epoxy once a few other parts are installed.