Most RV rental suppliers restrict access to downtown New York in your rental vehicle. Some of the streets in New York are very narrow, and the heavy volume of traffic makes accidents much more likely.
It is still possible to explore New York, however, since many RV parks are located on the outskirts of the city. Public transportation in New York City is very reliable, allowing you to leave your RV at the park and head into the city center.
Some popular choices near New York City include Liberty Harbour RV Park, Beaver Pond Campground, and New York City North/Newburgh KOA Holiday Park.