Not sure about 9A and 100 north. I can guarantee you are good to go 287 west to route 9 north... it is about 1.5 miles longer then the route you mentioned.
Route 9 is a little tight through town but more than passable. I wouldn't hesitate with any size rig.
If you forget anything, there is a real nice Shoprite just a mile outside the park.
There are a few Geocaches right in the park if you are interested in that. Bird watching is a big thing there as well.
Be sure to walk down to the point of the park. Real nice views of the Palisades, and the Tappan Zee Bridge.
There are some long term campers there, but it is a hidden gem that is open year round.
Water pressure a little high as well, need a regulator. If you are headed there in the Roo in your signature, you should have no problems getting into any of the sites.
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