Another private campground with hookups thirty miles or so south of these is Frisco Woods. It is usually less crowded than the three big ones in Rodanthe (Camp Hatteras, KOA and Ocean Waves) and has a few sites directly on the water on the sound side. None of the OBX campgrounds, public or private, have sites on the ocean; there's a sand dune barrier between the cg and the water on all of them.
If all else fails, other than holiday weekends, you can usually get into any of the four Cape Hatteras Park Service campgrounds without any problem. The one at Frisco is actually our favorite, public or private. These don't have hookups but do offer showers (cold water only) and restrooms with flush johns.