First up, this is great.
I kind of see a place for it beyond homeless people, though. A mobile, on-demand (subscription?) showering facility would be useful lots of places, and would help people like me, who get sweaty climbing a flight of stairs, feel more comfortable being active during the workday. Maybe you could even do a hybrid approach, where those who can pay do but those who can’t still have access.
Anyway. Cool project, makes the world better. Bravo.