I just stumbled upon the PortaPura treatment plant https://portapura.com/
It is aimed at the leisure market and the largest one they make is rated for 5 persons. But it is a very compact treatment plant working on the air blower principle but in a totally different form factor.
At only 800mm deep for the 5 person unit it might be of interest to someone with difficult ground / bedrock?
I am not in any way related to this product, just mentioning it in case so