The Dometic is a question mark to me- it is porcelain, which is nice, but it is glued together, and basically not repairable, other than a main seal, water valve and vacuum breaker. If any part of the mechanism fails, it's new toilet time.
One the one hand, the price is far less than the fully repairable Sealand, on the other, it's basically disposable.I prefer the 320, which uses a full sized elongated seat and lid.
As far as mounting pattern- the old Thetford Galaxy/Startlight models were oddballs, with bolts at ~11 and 5, Sealand uses 4 bolts at ~10:30, 1:30, 4:30 and 7:30 , most new models are 3 and 9, though Thetford Aria actually is 3 and 9 but screws in to the floor, well outside the mounting flange.
