Campgrounds on the beach in Cape Cod, MA are almost non-existent. There are some that are close. I think the closest to a beach is Scusset Beach State Reservation in Sagamore, MA. The campground is located right between the entrance to the Cape Cod Canal and Scusset Beach. There are no full hookups but there is water and electric at most sites. There is a 14 days consecutive limit. You can only get in with a reservation which must be made only with ReserveAmerica at-
1-877-422-6762 or online at www.reserveamerica.com.
Naturally all the campgrounds in Cape Cod are extremely busy in the summer season.
If you plan to travel in Sept., I would suggest Myrtle Beach where you can camp at the beach. We go there every year in Sept. to avoid the huge crowds and high temps.