Many of the larger banks have them, not so much as mobile branches but to use at events, e.g. fairs, etc. (rolling ATM's).
A bank I had worked for had one and used it right after Hurricane Andrew to assist customers when the regular branch blew away. With the on-board generators and satelite communications it did make a difference in many people's lives, as they were distributing cash and making loans the day after the storm. I don't have any details about the chartering though.
Integrity. With it, nothing else matters. Without it, nothing else matters.