We've stayed at the very bottom tip of the lake in Clute Memorial Campground in Watkins Glen town. Beautiful and convenient. Near Walmart.
Also check out Watkins Glen State Park campground. Never seen it, but it's a little closer.
If you can boondock primitive for a few days, fill your water tanks at home (or somewhere up there) and use your batteries and propane, you can park right outside the entrance gate to the rally. Grassy field area there. That's what we plan to do this year. We've done it before and it's so convenient being on-site! Everything you want is right there without riding back out for it or riding "home" after dark.
Call us if you have any questions.
Diane