The Best Spot
If you can handle nature in it's purest form you will really enjoy camping at Myles Standish, 45 miles south of Boston. You pay a nominal fee for a fully wooded campsite. This fee allows you free range of the 16 ponds, miles and miles of hiking, cycling, and equestrian trails, fishing, boating, etc. etc. You can spend an entire weekend here and not see another soul, if that is your desire.
Granted you must bring everything you need, food, toiletries, tent linen...if solitude and nature are your only goals, but for the experience of communing with nature, packing what you need is worth the trouble. Just remember to bring a lot of bug spray as the water and the woods are home to many an insect!
Have no fear though... you are welcome to bring your RV's and there are wonderful yurts that may be rented for those that want some creature comforts such as kitchenettes and indoor bathrooms. As this is a state park, the prices to bring your own "home" with you or to use one of theirs is still very inexpensive.