I think the OP is referring to Liberty Harbor RV Park. Yes we have been there...good for staying and having good access to NYC and the sites...good access to transportation, and a view of the Statue of Liberty...but it is just a parking lot with water and electric hookups. Close sites, gravel, but we were there to site-see, and go to the "Cake Boss" bakery.
They could also reasonably have meant Liberty State Park in New Jersey. I have never been there, but it looks to me on Google maps as though it would not be a particularly tricky approach for a class A motorhome.
Yes! Best time is to drive in from 10 AM to 230 PM. Traffic is a bear so study your route and read the sign! If you aren't in the proper lane well before you get there you'll be in VA or MD. I drove truck in and out of Port Elizabeth several years and tried to arrive after midnight. For you well informed, Liberty State Park is In NJ and you can drive to it. The RV park is easy to get into and all gravelled over, no grass just lined parking. (Makes for real fast dogs)BTW its NJ.