Dh and I are considering taking our 2 children on a 3 week RV holiday to the states next year. We are thinking about starting in San Fransisco and Finishing in LA with Yosemite, Death Valley, Vegas, the Grand Canyon etc in the middle. my Dc will be 11 and 7 and we are thinking about going in June.
We did Canada pre-children so not quite the same, but it was great. Only thing we struggled with was we were away for nearly 3 weeks and had huge suitcases and there was no where in the RV to store these so we were constantly moving them about. Also found renting one with a toilet useful and there were plenty of places on the campsites to empty it.
We booked the flights, some hotels and the RV with a company called Canadian Affair. We worked out a 7 day route and booked the campsites ourselves except for the municipal ones in the Nat parks which couldn't be pre- booked. It meant on those days we had to aim to be there for mid afternoon to ensure getting a pitch. Not sure if it's the same in USA. Cooking simple meals like Chili or BBQ ing was no problem. Some of the campsites were literally in the middle of no-where though so not much civilisation for eating out. Also, we were often the only ones in certain parts of the campsite so I do think you have to be fairly confident about being a bit vulnerable/exposed. Also, you can hear everything eg wildlife outside which is nice but not good if little ones would be frightened. I loved the freedom and it's a good way to explore the vast expanse of North America.
We have also done an RV holiday in Canada both pre-children and with a 10 year-old.
We did not have the suitcase problem because the company we rented with (Go West) provided storage for suitcases while you are away. After showing you round the RV they give you time to unpack and then you can put your empty luggage in their secure storage. Same thing in reverse when you get back.
I don't know whether they operate in the US or only in Canada but I would highly recommend them as they give a very good service.
We much preferred the campsites in the National Parks to the commercial ones and I am nearly sure you can book those but only if you are going in high season. I think the only night we didn't book was the first night and the last night but we managed to find somewhere OK.
We liked the National Park sites as you always got a fire pit and wood was available either free or really cheap so we could cook out over a fire. DD loved the novelty of that.
oh and the pick up/drop off points are MILES from the airports - $100+ on taxis. no realistic public transport, unless you want to take 4 hours getting to the site. look at hiring a car at the airport and driving to the site, then driving back to the airport - may work out cheaper!
Fanny When we went we were recommended not to try driving an RV straight off the plane when we would be tired and jet lagged, but to spend a night or two getting over the journey first. Then the company we rented with provided a complementary pick up from our hotel to the rental place. At the end they also provided a lift back to either hotel or airport as required.
Personally I would not do Death Valley in June. Just tooooo hot! I would also stick to California and not do Las Vegas, but that's just me! There are so many great outdoors areas in California along the coast, North of San Francisco and down Highway 1 and South to San Diego. You could spend a lot more time exploring and less time driving if you stick to California.