From the NYS Thruway (aka I-87) you would take exit 19 (kingston) to get to Rt 28 West. Take that for a bit, something like almost 18 miles to get to Rt 28A which goes around the Ashoken Reservoir. Note that this would be the second Rt 28A left turn as Rt 28A connects to Rt 28 at two points and it would be a lot faster to go past the Ashoken and then double back rather than take the long and windy Rt 28A around the reservoir. Anyway, once you hit Boiceville and coming down a long descent, Rt 28A will come up fast on your left before the downtown area. Take this left turn and go for a bunch of miles til you see Snyder's Tavern on your right (old house that is now an old bar). Then after you see the tavern, slow down as you'll want to make the next right onto CR42 at a wooden sign that says "sundown" at the very bottom and says Olive town offices or something like that. If you see the American General store, you've passed CR42... There is no sign indicating CR42 intersection but you look down every right turn, you will see a blue CR42 on the road.
Then you'll have to go for another 5 or 6 miles or so until you see a bridge with Merrill field on your right. After this bridge, you will see a bunch of dirt parking lots in a row, this is Sundown, again on your right hand side. The campsites are generally not far from the road so you may see tents and pines and perhaps the portopottys there. We'll be probably all gathered on the sites a few parking spots down from Merrill field, where there is a kiosk there. Camping is free and first come, first serve.
If you google maps the town of Olive, NY, you will see Rt 28, Rt28A and CR42 which is shown as Peekamoose Road. The campsite is closer to what it says "sundown" there but not entirely that far. There isn't going to be any cell reception at the campground and probably spotty reception anywhere in the catskills from Kingston.
Jay