Boston has all sorts of stuff to see and do--many excellent museums, Old Ironsides and other historical sites, etc. You should have no trouble filling a day and a half. I've enjoyed the Museum of Fine Art and (though it's been a long time) the Science Museum and the Aquarium. The Van de Graf generator in the Science Museum is impressive.
If you like Mongolian barbecue/create your own stir fry sorts of places, Fire + Ice is quite decent, though a bit cramped.
Avoid if at all possible driving in Boston proper, doubly so with the trailer. It's not a fun city to attempt to navigate by surface street, to mention nothing of the fun of parking (and paying for the privilege). Public transit works well; the subway is not too hard to figure out. The tunnels in the area (which mainly means I-93 and I-90 under the city proper) do not permit propane. Apologies if you're already well aware of these things.
Your last day's drive home looks very long. I might think about splitting it up, and I don't mind fairly long drives. You know your own limits better than any of us.