I assume you will travel from Mystic to Vermont on Route 91. You will go by my house, only a half mile from the highway in Bernardston, MA, last town in MA before VT. Stop at the Vermont visitor's area five miles north of the border. The building and contents are worth the view, a mini museum of what's in season in Vermont.
I suggest you camp at either Ricker Pond or Stillwater in the Groton Recreational area, just south of Montpelier. The area is the largest state controlled recreational area with six or seven separate recreational parks. There are miles of old narrow gauge railbeds running throught the forest. There is even a ghost town from the 1900's lumber boom.
Call for reservations and try to get number 18 in Ricker Pond. The site is private, over an acre and on the water. Ricker Pond limits horse power to 5, so its quiet. Groton Lake, where Stillwater is, is much larger, has summer homes and the annoyance of water skiing. But is dead quiet at night and is beautiful, too.
here's a helpfull link
http://www.vtstateparks.com/htm/ricker.cfm