Effort vs return just isn't there for gas capture... all that infrastructure, including waste storage. Yikes.
I'll say I started with a composter, we used it for #1 but not for #2 except a handful of times. By the time we were getting close to our house selling, I knew it was a dead end, we _needed_ a flusher. A few days before we left I had a flush toilet (Dometic 310) installed. Bullet points time:
- If you already anticipate/need to deal with a grey tank (with sink water in it), dumping a black tank is going to be the same process, just pull another lever.
- Consider _all_ the things you use a toilet for. Not just pee, not just poo. How about feminine care? How about it you're feeling a little nauseous?
- Long Long Honeymoon introduced us to the concept of a bidet- a device that very much helps us cut down on showers while generally improving hygiene. IMO, bus life is better with one, not something you're going to have on a composter.
Keep in mind that some people went from having a black tank to a compost toilet and consider it an upgrade. We do not understand it, so they'll have to make their case.