In Las Vegas, if you plan walking on the strip the Circus Circus RV park has the best location.
Price-wise KOA (I think it is called Sam's) RV park offer best rates.
Mind the dining on the Strip is extremely expensive and if you go to satellite casinos, they offer lower prices.
Before reaching Las Vegas, consider overnight stop at Valley of Fire. It is really worth it.
From Vegas to Diego there is not much to stop. In Baker you might stop to take a picture of tallest thermometer in the World.
Few miles East of Barstow you can visit Calico Ghost Town -western park.
The route is stuffed with up to 17 miles long grades, so if you plan to take it midday, make sure your cooling system is in perfect condition as 100F is cold day there even in September.
Also remember that California does not allow bringing fruits and they might check your coach for moths. The agriculture check station is East of Barstow, but they are building new one close to the state line. Don't get upset if they hold you there for some time.
