looking for a good campground between boston and cape cod

Normandy Farms is a great campground. But, it is a little higher in price and is not the best location for the Cape. The Boston/Cape Cod KOA is a perfectly nice, wooded, campground that is in a great intermediate point between the two destinations. There are also a number of campgrounds in the Plymouth area (haven't used them yet, but know they're there).

If using it as a base for exploring the two regions, I'd likely use the KOA.