We really like Lee's Ferry campground on the Colorado River. It is usually quiet, and it is great fun to see the rafters preparing for runs down the Grand Canyon. It is a no reservation campground, but we can generally get a site. There are some interesting historical sites in the area too. Dry camping only, but cheap. Another interesting place a bit out of your way is Willow Beach, a NPS site on the Arizona side of the Colorado south of Las Begas. I am pretty sure it has electric sites. You can catch a power raft trip upriver to the Hoover Dam - very scenic. For Bryce, we like the park campground best, but Ruby's Inn (private) isn't bad. The park bus picks you up right across the street. Go up to the end of the route then walk back, stopping at all the overlooks. Alternately you can just ride the bus between the spots. Also you could check out some of the Utah State Parks, especially Goblin Valley, Horseshoe Bend, and Kodachrome Basin. All are great. As for SLC, I recommend the KOA on North Temple. It is right across the street from a light rail that will take you to downtown and the historic sites so you don't have to try to park the RV downtown. The light rail and buses are free in the downtown area.
As an aside to Tom, I think you may be responding to the wrong message. The OP doesn't say anything about Grand Tetons.