Sounds like a great trip. Down in the Boston area there are few options. Two have been mentioned here. Normandy Farms is a very large Campground with quite a few amenities, it is located about 3 miles from Foxboro stadium. The Minuteman campsite is nice, has received some upgrades in recent years the roadways are narrow for larger ubits, it does have access to the train.
There is another option Salisbury State reservation is a large stae facility, does not have sewage, does have a dump station. It is located on the ocean and beach, directly down RT 95 to Boston.
Of course when you are in Boston a Red Sox game is a must, a tour of the City on the Duck Boats, a stop at Fanuael Hall, Restaurants in the North End or in the Sea Port District. Do not forget though to make it over to Lexington and Concord, or upto Lowell and Lawrence where the Industrial revolution began.
Sorry for rambling much to do, so little time.
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