(From a previous post)
"I used MCCA Mail Forwarding in Palm City, FL as my official address for a number of years. From this address I obtained my FL drivers license, registered and insured my boat and automobile, and even used it when I renewed my passport. Never had a hassle.
I think the key to all this is being able to show a street address. A P.O. box is not a street address. However, you can have your mail sent to a mailbox rental place for which you will have both a street address AND a box number.
This method always worked for me."
Not sure MCCA is still doing business. If not, consider St. Brendan's Isle. They've received consistently good reviews from cruisers.