It's best to avoid going through NYC on I-95 with the motorhome. The road will beat up the rig, and the toll over the GWB is something like $40+. Definitely better to use I-81 to I-84 to I-90.
If you do decide to use I-95, note that you must use the upper level of the GW Bridge. Just follow the trucks.
Also note that in Boston you are not allowed in the tunnels with propane. That is, I-90 and I-93 through downtown Boston. You need to use the loop around Boston along I-95/128.
Finally, my choice for camping near Boston is Wompatuck State Park in Hingham. It's about a 10 mile drive to the Braintree T Station from where you can catch the Red Line into Boston. The only hookups available at Wompatuck is 20 amp electric. They do also have a dump and fill station. The park itself is interesting as it was a naval munitions depot during WWII and Korea. I spent a lot of time there when I lived in Quincy.
Allen "Monkeywrench" Freeman, Full-time Nomad
2011 Itasca Sunstar 35F AKA The AdventureMobile
Dragging around a 2013 Ford Edge with a Blue Ox Alpha Tow Bar and an RViBrake3