"Or you could catch 84 and cross at Newburgh and then come south on 9 (I have never been that route with the camper so not so sure...but 9 is a major roadway)"
We did this last month. South on 9 was easy - road a little windy but good.
South of Croton, Ossining and Terrytown traffic can be awful and the short runs through town are skinny.
Your GPS will really, really want you to take 9A. Don't! Of course, we are 12'10" but if I recall correctly, one bridge is 10'9" or so. Better to suffer through the traffic if you need to take the RV south.
Croton Point Park is very nice.