I have heard that UPS is a great service. You get a street address, not a PO Box. Should be good for DMV. http://www.theupsstore.com/mailboxes/Pages/personal.aspx
What we did when we had a mail forwarding service in FL was change our address. on credit cards and other accounts in plenty of time to get 2 of the following documents at your new address:
Proof of Residency Acceptable Documents for NC DMV:
Listed below are acceptable documents you can use for a U.S. Citizen:
Any document issued by this State or county, city, or the federal government;
NC Vehicle Registration Card or title;
NC Voter Precinct Card;
Military Orders/Documents;
Utility bill or cable bill;
Housing lease or contract, mortgage statement, property or income tax statement;
Preprinted financial statement;