Indeed. Unfortunately "out the back" for me means through the hull.
True, but given the thousands of Portapottis installed in boats I'm sure Thetford are aware of the market. Thinking about it, you can get a floor plate for the new Excellence specifically designed to secure it to boat floors, so they know we're buying.
I guess it's a matter of scale - they have a small range & it must cost a lot to launch a new design. But I reckon it would be worth their while. Especially if they marketed it as a boat toilet. A ceramic bowl would be a great idea too...
Had a look. They do a flash-looking cassette with a ceramic bowl, but it's a rear-access job.