Hey D Greene,
My wife and I just stayed in Watkins Glenn in October. Had a greta trip despite the colder weather. Had to unhook the water hose one night because we got freezing temps.
We stayed at the Watkins Glenn KOA (Watkins Glen/Corning, NY KOA Campground Big Rig RV Park
) and it was a great stay. We stayed in Lot F181 which was a great spot. F180, F181, F178, F179 (look at the site map) are back in premium lots and you feel secluded in them.
The folks that run it are really nice folks and very helpful. You will be close for short drive in to the state park for hiking and the city of Corning for the Glass Museum tour (vist this if you have time). We also spent a day In Ithaca which is a great college town.
Hope you have a great trip..