I think Brett Weston had a darkroom van that he used for loading his 11x14" holders and processing film. You might see if you can find any info on it.
Permawash will cut your wash times substantially, and you can use 5-7 changes of water in place of running water. I think during a water shortage Ansel Adams determined (using a residual hypo test, I'm assuming) that 7 changes was good enough for fiber based prints. The setup was 7 trays in a long sink (stacking would be the obvious way to save space), and the system involved periodically dumping tray 1, moving the others up, and filling it with fresh water and moving it to position 7.
If you wanted to try to print in a van, you could look into a slot processor.