I looked into some of this stuff when we were moving across the country and temporarily had no actual permanent address (living out of AirBnBs) including no home under contract, and it would have been very nice to set up a PO Box and local bank account.

I couldn't figure out a way to do it. Even looking at services aimed at people living in RVs didn't seem like it was going to work. For one thing, I couldn't get a PO Box without a home address, LOL.