There are no RV sites with electrical in Yosemite National Park that Iím aware of. Also, the valley floor does get quite hot during July but usually not near as hot as August. Outside the park there are a couple full hookup RV parks, the closest is probably on Hardin Flat Rd. You also might try Yosemite West who has cabins but Iím not sure about RVís.
Steveís post about the Pines campground is correct but you need to check which will accept animals (check that for all CG's).
If you have a small RV my favorite is Tamarack Flat but has been first come first serve in the past.
Porcupine Flat is another great first come first serve small RV CG located between Tuolumne Meadows and Crane Flat.
Tuolumne Meadows is the most beautiful spot in the park IMO and the CG offers a high altitude terrain that is at least worth looking into. But itís a long drive back to the valley floor. Mosquitoes might be an issue here in July. It has a small store and restaurant plus gasoline (no diesel) and the best fishing for access from the highway. There are some great hikes in cool weather from here at 9000 feet.
Another fine CG is Bridalveil located on the road to Glacier Point. Also a first come first serve camp but another high altitude CG that is cool in the summer.
Most of the other campgrounds are by reservation and book quickly.
If you want more info on the area just PM me and I can give you some suggestions.
I donít recommend this spot but itís fairly close unlike most of the others outside the park.
http://www.reserveamerica.com/camping/Y ... kId=260571
The state stocks the river here for some really good fishing for large plants.