For RV camping near Yosemite Valley, Indian Flat Campground is quite good. It has full water + electricity + sewer hookups. It's also about a 5-10 minute drive outside the park entrance, and I didn't see any RV camping on 140 that was closer, so if you're coming or going on that route it's very convenient.
One major complaint I have about this campground, though, is the showers. There's a single shower unit in each of the men's and women's bathrooms, and two additional units on the other end of the bathroom building. These are the ones you want to use. You do NOT want to use the makeshift outside shower units behind the bathroom building. All you get are three walls, a door, two hooks, the shower head and controls, and a concrete floor. There is literally NOTHING else - no roof, no mats, no benches or shelves. There isn't even a drain in the floor - the water runs out a small gap between the wall and the floor. And if you're showering in the evening, make sure that you're done before the sun goes down because there is no illumination provided other than the sun. I have attached some photos of this shower area so you can see how bad it is.
If you have an RV, just take your shower in your unit. Fortunately, this is pretty doable thanks to the electricity/water hookups.