I usually post this video for composting toilet talks. This video is from the "Gone with the Wynns" series. They started the series in a motorhome then moved to a large cat sailing vessel, and use their Nature's Heads on the boat as well.
Air Heads are better if space is tight as you don't have to include space for the hinged top as you do with Nature's Head. The top just lifts off from an Air Head.