Please be aware most RV Parks close by the middle of October in Maine.
Normandy Farms is close to Boston.[Lots of historical things to see in that area] I think that is open most of the year with limited service. We like Lake George RV Park in Queensbury, NY. there is a lot to see in the Adirondack's. You visit Lake Placid. Ledge View RV Park has less to offer but much less expensive. In Maine just below Portland our favorite park is Bayley's RV Park in Scarborough, ME. [Big Rig friendly] There is a lot to see and do in that area. I will warn you RV parks up here are pretty expensive. They have to make all their money in 4-5 months.