Yes, there are hundreds of stories about the Dometic 300. But every one of them ends by saying that the Dometic 310 is dimensionally equivalent and was a drop-in replacement that took about 20 minutes.
It is the Dometic 320 that is deeper and needs more clearance from the back wall. If you haven't already installed a new Thetford, just get a Dometic 310, not 320.
Sticks and Bricks: Raleigh, NC
2008 Cherokee 38P: at Ivor, VA permanently