I replaced my 30-year-old terlet with that Dometic 310. Huuuuge improvement. Water line was in the right place, but the mount wasn't. Needed to get Dometic's riser kit that attaches to the existing flange and puts the mounting bolts in the right place. Puts it up another 1/4".
The stuff I found under and in the crevices of the old terlet was pretty nasty (in 1984 they put the toilets over the carpet, and there are lots of places under/in the old terlet for things to get "lost" - feminine hygiene products in particular). You're welcome.