Check out the map at, http://www.blm.gov/style/medialib/bl...0for%20web.pdf
It has all the campsites. 2 years ago a lot of the camping on C was hard to find with tamarisk overgrowing the landings. Good news is that there is not a lot of people who float C section. You will loose 3/4 of people once past A.
I like 2 nights in B and 1 in C. Dutch John has services to shuttle the car.
For camping the night before, Google Flaming Gorge recreation area. There are plenty of campgrounds. We stayed close to the visitor center in the middle of July and basically had the place to ourselves.