Just a warning - both Arches and Grand Canyon South will be hot in July but that's no reason to stay away.
Arches only has a campground with no hookups so I wouldn't advise that in summer. In Moab itself there are plenty of RV parks with hookups. Also, nearby Canyonlands Nat'l Park has a wonderful campground and some sites have electric.
For Grand Canyon, Trailer Village IN the park is the place to go. I'd make reservations there first and plan the rest of your trip around it. It's very popular.
For Sedona - which will be hot also, we always stay in Cottonwood at Dead Horse Ranch State Park. It has electric. Lots of things to do in the immediate area and an easy drive to Sedona.
