Parking near Boston

A truck and a hybrid camper, you've got more options and I wouldn't limit yourself to an MBTA parking lot or unhitching at an RV park.

Fenway, USS Constitution have oversize vehicle / tour bus lots you could probably get into. Or you could probably just park on street in the seaport/world trade center area. Maybe Assembly Row or the Home Depot near it.

Of course your rig won't be much bigger than the u-haul/ryder truck rentals that get double parked all over town before labor day, so you might be able to just blend in.

Crowe wrote:
I believe the commuter boats are no longer running from Quincy

Per the Massport website supplied above they are still running. However, if the OP is heading to/from the Cape, Hingham may be a better option. Again, a quick phone call to Massport can answer the question.

Their website says (mistakenly ?) that they are running to Quincy, but if you go to the boats map, they only show, and give information for the Hingham service. An in-law had told me, quite a while back that there was a problem with the dock/wharf at the Quincy location. Knowing the way things operate up there, it appears that there might still be a problem. :B
I think the OP could find a Walmart,supermarket,mall parking lot, with access to the the T, and be good to go.

I believe the commuter boats are no longer running from Quincy

Per the Massport website supplied above they are still running. However, if the OP is heading to/from the Cape, Hingham may be a better option. Again, a quick phone call to Massport can answer the question.

I believe the commuter boats are no longer running from Quincy - only from Hingham, on the south shore. Parking in Quincy, or somewhere closer to downtown Boston could work for you. I moved to Fl. from Quincy, many years ago. :B

"Pass Boston" from where to where? That might help figure out a spot. As far a Quincy goes, it depends on how far you'd have to walk. This might be a long shot, but a phone call can give you an answer. There's a water taxi service also in Quincy. You can ask if there's parking there or a convenient location near the terminal. It takes you right to the waterfront near the aquarium and not far from Quincy Market/Faneuil Hall. https://www.massport.com/logan-airport/to-and-from-logan/water-transport/

Just looking and found a walmart in quincy. Walk to the bus/T? Is this a good idea or not?

I knew a couple of guys born and raised in Boston when I was in college. They swore that the roads in Boston were created by some guys driving a paving machine, following an old cow wandering around. I was in Boston on business once. I believe it.

I would also suggest contacting Normandy Farms in Foxboro. It is at the intersection of 95 and 495 on the south side of the city. They may let you store the trailer for a day and take the truck to the commuter rail station in Foxboro or maybe the Red Line subway in Quincy.

Parking is at a premium at both the subway and commuter rail lots. In typical Mass. planning, they didn't anticipate how many people would use mass transit. The lot in Braintree and at Riverside are full by 8:00 am. The person you talked to at the T has never actually had to commute via the T.

If I were doing this based on the fact that I've lived here for 50 years, I'd grab a spot at Normandy Farms or Minute Man, drop the trailer and drive to the commuter rail to park just the truck. Alternately, you could grab a cab from the CG to the commuter rail station. I seriously doubt that you'd find a parking spot for the truck and trailer at any T lot.