Idaho Power has several campsites in Hell's Canyon with electric and water. They are first come / first serve, but that shouldn't be an issue in the fall.
Stanley has an actual rv park, and lots of dry campsites scattered around. Plusses are that you have the Sawtooths front and center. The Yankee fork gold dredge is open for tours, and there's a few ghost towns on the same road. There is also a hot spring that flows into the Salmon river - it's fantastic! (Look for cars parked on the road with people changing into or out of swimsuits. Idahoans are a conservative bunch, except for when it comes to hot springs.)
There is more great camping on Cascade and Payette lakes. McCall is a neat town.
I'm sure others will be along shortly with more ideas.