Get to 81 North via your favorite interstate. I come up via 476 when I go to Pocono. There are hills, might as well hit them at 75, well into the torque band. My trailer is super stable, I still probably roll a bit too fast
To stay on the interstates, take 81 to Binghamton, hang a left on 17 and take it to Horseheads. Take 14 N to Watkins Glen.
Your toughest hill will be going from the vibrant metropolis of Watkins Glen up to the track. Your best choice is to go up the hill at the Valero Station (329) toward the Seneca Lodge. Instead of hanging a right to go to the lodge keep going straight to Rt 16. Turn right on 16 and follow up to the track.
The other route, 414, looks nicer because it is 4 lanes, but it goes up a steeper gradient - measured by the wheezing of my truck.
From Allentown, Pa you should be within 3 hours of the track.
You wouldn't happen to be doing the Group 52 event, Oct. 8,9 - would you?