If you're looking for a full-service RV resort, there are a couple that I know of in the area, but not right on Seneca Lake. There's
Junius Ponds RV Park, which is a bit north of the lake. Unfortunately it is right next to I90 - the NYS Thruway. So - lots of highway noise. I've never stayed there. A bit to the west is
the Canandaigua KOA. Again, I've never stayed there.
It's a beautiful area. I have a seasonal tent site on the shores of Cayuga Lake, and I spend about 45 nights every summer there. I keep a cruising sailboat on the lake, and I sail just about every day while I'm there.
There really aren't any sizable towns along the shores of Seneca Lake - east or west. Geneva is at the north end, and Watkins Glen is at the south end. If you're into estate wineries, you'll be in heaven. There are hundreds of them in the region, and some of them have world-class wines. Hiking, biking, boating, fishing are all very popular activities. If you give me some idea of the kinds of activities you like, I may be able to give you some tips.
-Speak