Recreations Vehicles have now taken on the use of composting toilets as an alternative to water and chemical based system. The smaller composting toilet system are very suitable to the confined space.
There are however, restrictions on post composting locations and often the partially composted end product has to be dispose of as rubbish, so not completing the cycle.
But the waterless benefits are still a good feature allowing drivers to go to remote locations for extend period of time compared to water and chemical based system.