I would follow the directions you have to the Cape May - Lewes Ferry and then the Garden State Parkway, as noted, up to Exit 129 for the NJ Turnpike. I-78 is the Newark Bay Extension of the NJ Turnpike at Exit 14. After paying the toll drive straight until you come to the first stoplight. After the first stoplight begin to merge to the farthest right lane. At the last stop light before the Holland Tunnel, make a right onto Marin Blvd. Follow this road until it ends; the office is on the right. - See more at: http://www.libertyharborrv.com/directions#sthash.NaIqZAMo.dpuf
Marin Blvd. is a snug urban street, but quite do-able. Try to catch the view of Lower Manhattan at sunset from nearby Liberty State Park.