Fwiw, I wouldn't want to tour any major city in an RV. I have trouble parking my crew cab truck in a lot of places in some cities, and NYC is probably the most conjested.
Otherwise, rent from a major carrier like Crusie America and you'll be good.
Remember , you don't always need a campground, you're in a RV and can stop about anywhere for the night, if you're out in the boonies.
Presume you're planning on staying on the east coast?
America has a lot to see everywhere, but IMO, NE and eastern seaboard is great, then there's a lot of not much to see if you're on a 1 time trip until you get out west, which is days of driving. Just think about miles vs sights you want to see.