We like Scusset Beach (state Park). Water electric with dump station. @ weeks ago the dump station was closed and I heard they are still having problems. But Scusset is probably totally booked for July and August.
Sweat Water in Brewster is very nice, wooded and full hook ups. Usually can have a fire. It is on a small lake, but no swimming or pool at the campground. Close to bike trail. We like the full hook up sites.
Cape Cod Resort in East Falmouth has small sites and we found crowded, our neighbors campfire kept setting off our smoke detector! They do have 2 pools and a lake for paddle boating.
On the Bourne/Plymouth line is Sandy Pond which offers full hook ups and allows campfires. Small swimming lake and a small pond for fishing. Nice wooded trails for hiking.
If you have problems getting reservations on Cape for July, try the Middleboro/Cape Cod KOA.
Being from the area we usually leave the cape area in summer to avoid the crowds. If you need more suggestions, just ask. For Memorial Day weekend we stay at Normandy Farms in Foxboro, but that is about a 40 minute ride to the beginning of the cape.
We have friends with a seasonal at Bourne Scenic Park which is right on the canal. They do not have full hook ups, are right under the Bourne Bridge, so traffic noise. We bike the canal trail all the time so pass by the park. We attempted to make a reservation and spoke to the representatives at an RV show and they were not very friendly or helpful, so good luck if your call them. They do have 2 new pools. The camp ground is mostly seasonals. Nickerson State Park in Brewster is another nice campground, but we only go to hike since there are no hook ups.