To avoid Boston you can take either 128/95 or 495 around the city. Where you are headed will determine which one is better. Many prefer 495 even if it's further out. Both have nasty traffic, especially at rush hour. If you don't have campground reservations I'd make them, especially for holiday weekends. You will be hard pressed to find open sites last minute. You trip sounds quite ambitious but also vague-it's a bit hard to help without at least some idea of how long you want to stay in each spot and what you'd like to see. Also keep in mind we talk about distance in terms of time, not miles.