Everybody's making this way too complicated and expensive. Of course you can (and should) use a composting toilet. We, too, never used the toilet that came with our RV.
I bought a
Cabin Can just because it's very attractive, and I'm a girl and like that kind of stuff.
I seriously objected both to dealing with disgusting black water, plus the usual chemicals that go along with it, AND the pee bucket that allows urine to so beautifully "ripen" with time, that comes with Nature's Head, et. al. (Had never heard of the "vinegar cure" though.)
This one uses NO electricity at all, requires no installation of anything.
I will be blunt: We pee in the shower stall. You guys come with pre-attached hoses; use 'em, and just develop a system for quickly rinsing the stall afterwards. I attached a spray hose to the existing water inlet for the toilet. It reaches the shower. You could also, of course, just use your detachable shower head, but that's a bit more hassle. Saves the extra weight and possibly smell inside your composting toilet.
This is great for the girls; I LOVE mine. Cut the bag off and the other end of the tube fits right in the shower drain. Then I use the hose/nozzle I installed to rinse the urinal. Off course, the guys can use this, too - saves possible splashback from the shower floor.
The rest couldn't be simpler. Your basic 5 gallon bucket, lined with a usual size kitchen trash bag, fits inside the Cabin Can. The key to "no smell" is PEAT MOSS. I learned this the hard way when I tried to switch from using a mixture of peat moss and wood chips (the stuff that's supposed to be rodent bedding; you can even use cedar chips) to wood chips only, and that was a mistake. :E
If you use all or at least half peat moss, your toilet will smell pleasantly earthy. Just be sure to cover up after each addition completely.
The contents will start to settle, but once your bag finally is really full, tie it up and dispose of it. You can also
actually compost it if you wish, but that's usually impossible to do if you're moving frequently. For that reason, I refer to mine as a "dry toilet", rather than as a composting one. And no, this does not need to be vented.
And as someone else mentioned, now you can use both your gray and black tanks for gray water. Put a gate valve where there's only a screw-on cap now, keep it closed (unless you're connected to sewer), but leave both the gray and black gate valves open.
