Hi,
Yes, I have done a tour in a motorhome through California and Nevada, albeit a fair while ago.
In my opinion, because of the good value to be had from staying in motels I think a car is a better option to be honest.
We stayed mainly in KOA (Kampgrounds of America) when we went and you end up paying a fair bit to hook up to their water and sewage pipes when you stay there, as well as a nightly fee so it ends up being a bit more expensive than you may think, especially as you'll get very poor mpg from the motorhomes (RV's) themselves. There are loads of KOA's around and of course you can stop anywhere but you will need to stay in an RV park regularly just so you can empty your waste tank and replenish the water.
Another issue is also if you drive in a city - we picked ours up in LA and it's not easy to drive a vehicle that's about 20ft long in a major city! Parking it is something else altogether!!
Personally I think it's an expensive way of seeing the country.
If you're happy staying in Super8/Comfort Inn style places you can get them very cheaply and car hire is also quite reasonable and most cars will do a lot more mpg than the RV's!
That would be my recommendation anyway!
Cheers,
TC