Katherine, it all depends so much on where you will be. For instance, if I were anywhere near NYC or DC I would definitely spend the 4th of July there. On the other hand, if I were in Boston, I would go for one of the lovely rural towns west of Boston. I have on several occasions spent 4th July in St Paul and once (I think) in Boston. St Paul, where family live, they have a small localised parade, almost like a small town.

So where will you be?

Do a little research and see if you can find an RV park close to a railway station in a city in NJ, a short way out. I am not aware of any in that area, but it is worth getting the atlas out, and seeing which places there are, and see if their tourism centres bring up any RV places. I would doubt very much if any are quite close to rail or the city. Could spend quite a bit on rail fares and time travelling.

Of course you could base yourself on the northern side as well, if your next destination is Rhode Island.

Lifey