Not sure Myrtle Beach is what you are looking for. But they do have campsites just across the dunes from the beach. there are walkways across the dunes. You can get sites less than 50 feet from a dune crossing to the beach. the dunes are high enough that you really can't see the beach at every CG except Apache. you can sit on your site and see the beach from many site at Apache.
and yes "some" CGs have traffic all night. but PirateLand strictly enforces quiet time, and there is no crusing after quiet time.
Also. IF a small quiet CG is what you want. you could try Surf City Family CG on topsail Island NC. Again, Just across the dunes from the beach. It is VEREY small, and really all it has is a GREAT beach. It is about 45 minutes North of Wilmington NC. We really like it.