Yes, the Patriot act does hold lenders to a higher standard for customer verification. Credit cards are very often used to illicitly move money and fund nefarious conduct. As a practical matter, someone living in a post office box is going to be very hard to collect from should they decide to stop paying. Combine the two and getting credit without an address is going to be difficult. And using the street address for the PMB company isn't going to help. All bank software is sophisticated enough to ferret out those addresses as being mail forwarding services. Like it or not, it is a problem full time RVers have to live with.
