The KOA is really large, and looks like the parking area of a drive-in movie. No trees, lots of sand and gravel, and sites very close together. Beach access is good, but can be a pretty good hike if your site is near the back, or front depending on how you look at it :) . The KOA and Camp Hatteras are very similar with respect to sites and spacing.
We stayed at Ocean Waves where the sites are also close, but there are trees and grass and altogether a more pleasant RV park. It's a little harder to get to the beach as you don't have a boardwalk to use. And it usually fills up really fast, and stays full.
You won't have any trouble with a large 5th wheel at any of the RV parks.