Are there any surface parking lots in or around the Boston historic area - no garages - one that I could park a Class B in safely for the day? Or adjacent to the "T"?
Most of the "T" parking areas are garages. How tall is the B? No open parking left in the city-when they took the El train structure down they turned it all into greenway. Looks lovely but took away a lot of parking. However, there is at least one, if not two, garages that have oversized parking areas. Google "Boston Parking Garages" and it will come up with a list of them. Parking heights might be listed but they are manned most of the time so you can call and ask. The other option is parking in the oversized area at Logan, but then you'd have to get into the tourist area. Easily done by cab.
On edit: There's a place called "Hilton's Tent City" over near North Station and the old Boston Garden. There used to be open lots over there. Call Hilton's and ask if they are still there. You are a bit outside the area where you want to be, but again, you should be able to take a taxi. No guarantee of availability in any of the areas but at least you know where to look.