Boston has excellent public transit. Commuter rail goes to the suburbs. From the North and South commuter rail stations, you can get the T to just about anywhere in the city. No matter where you stay, you'll need to travel to see everything. Boston is compact, but some of the more famous sights or sites are in other cities nearby.
Freedom trail, Paul Revere's grave, and the USS Constitution are walkable in the North End, but Lexington and Concord are a drive away from the city and you need transportation. Harvard and MIT are across the Charles in Cambridge but both on the T routes. Some of the more famous buildings at Harvard aren't as spectacular as you might hope. Harvard Yard is fairly nondescript though worth a visit. Some of the others, particularly Memorial Hall are memorable.
The cool part is that there are RV parks near some of the commuter rail stations and hotels near all of them so you can easily hop into town to do your sightseeing and then ride back out to your park. Fairly painless if you dodge the rush by heading in a little late in the morning and staying in town for supper before heading back out.