I'm in Portland, Oregon.
I've got a used AirHead composting toilet (marine size). Just finished a thorough cleaning of it, replaced the intake filter, replaced the fittings and clear tubes on the level indicators on the liquids tank, as well as the extra liquids tank (with lid). I'm including extra material to make your own intake filters, as well as the brackets to mount it to the floor. This is the model where the liquid tank attaches to the base, and does not require it's own brackets to the floor. Also includes a lid for the solids tank--nice for when you need to carry it somewhere to empty it. The crank handle is on the right as you face the toilet, and the vent connection is also on the right.
More info and photos on my CL listing here:
Size (very compact, ideal for small spaces)
17" front to back including liquids tank (15" without the tank)
16" wide including crank
If you're considering a composting toilet for your RV, boat, van conversion, camper van, tiny house, you're probably familiar with both this one and the Nature's Head. I've got the Nature's Head in my camper, so can give you a quick list of the differences between the two.
The AirHead is smaller (about 5' shorter) so fits in smaller spaces, and also requires zero clearance behind it. The AirHead has a regular toilet seat, and lid, vs the Nature's Head having just a lid. Not sure which is better, but the AirHead feels more like a normal toilet. The AirHead liquids tank can be removed without opening up the solids container. I suppose that's a little nicer, but not a huge deal to me. If you don't like looking at the inside of the solids container every other day when you need to empty the liquids tank, this is a nice feature. The AirHead liquids tank is not translucent, like the Nature's Head. So you don't visually see all the urine in there, just in the level indicator tube. The AirHead is better sealed. There's a gasket between the lid and the seat, as well as between the seat and the top of the toilet. The 12v fan on the AirHead is located at the far end of the tube (so you'd mount it against the wall/ceiling you're venting through) rather than agains the toilet. This makes for a cleaner install, since on the Nature's Head you've got a wire that you have to plug into the toilet for the fan, rather than it being hard wired. You have to unplug it every time you empty the Nature's Head solids bin. Due to the way you remove the top off the Nature's Head (open it up, then slide the half-barrel hinge off the side) you need a lot of clearance to do this without removing the whole toilet from where you have it installed. I had to install mine 6" out from the wall, wasting a lot of space. The AirHead requires zero clearance, you can mount it right against a back wall. The AirHead's solids tank is also nicer for emptying - has handles on the sides, and is round without the lip at the top that catches your compost as you empty it (one of my pet peeves with the Nature's Head). Main downside to the AirHead is usually the price (although if you're buying this used one, you'll eliminate that problem!. With the extra liquid tank, this one would be $1,074 if you bought it new, plus $54 shipping = $1,128. I'm asking $850 OBO.