Im giving Goodsams trip planner a try from Ashland, NH to Virginia Beach, VA and it's going right thur the middle of NYC., What? I'm sure they have't tried that
Add even stronger warnings. When we drove across the GWB - summer 2015 - there were strong warnings that propane cylinders were not allowed. They are certainly not allowed in the tunnels.
Tappen Zee ( I-87 / I-287) is the southern most point that an RV can cross easily.
Set a stop just before the Tappen Zee Bridge and that should route you around NYC.