This probably won't get you past the requirement of utility bills in your name at that address to get a "Real ID" that allows domestic flights without a passport, though.
Same thing for getting a PO box, you need a physical address first. The post office will tell you the same thing, to use the address of a homeless shelter.
The folks writing these laws do not live in vans, and do not care, nor even think about the impact of their actions on folks with alternative living arrangements / folks poorer than they are.