We did the OBX trip a few years ago (Detroit area to OBX) but we split it by going to DC first and then on to OBX.
In addition, since we're not retired, we did the interstates all the way...so I guess I'm not much help. LOL
OBX is really cool!
If you're looking for a place to stay try
Camp Hatteras. You can even get a site about 30 ft from the beach.