For those with RVs, this is a good website for RV parks and campgrounds. We use it frequently and have found the reviews to be factual and fair:
www.rvparkreviews.com/regions/california
This is for National Parks non-concessionare campgrounds:
www.recreation.gov
Many NPs contract out campgrounds to concessionaires and they have their own websites. Those are NOT on recreation.gov. So before you reserve, go to the actual Park website (url will start with www.nps.gov) and search for campgrounds there & follow links. Many have booking windows and the popular sell out FAST! We haven't been able to get a summer site in YNP in years.
slalom Your DH is absolutely right! Never attempt to drive an RV of any kind in SF. On the freeways through the city, fine, but never on city streets. I actually think it's prohibited in areas. There are a few RV parks just outside the city (use the RV park review link). Park the RV and either use public transit or Uber. I think one or two of them may have shuttles, at least they used to offer them. They're pretty much parking lots with hookups, not scenic camping as they figure you're there for the City. We live close enough to just drive in, but have stayed at the SF RV park in Pacifica. It was nice enough 15 years ago but haven't stayed there since.
Kath Yosemite Valley campsites will be long sold out by now. You can try for cancellations, but I wouldn't count on them. There are plenty of places outside the Valley. Also, the campgrounds in YNP (Yosemite Natl Park) are 'dry camping', meaning NO electric, NO sewer, and NO hooking up to water supply (it's fill and disconnect). This is true for most national and state park campgrounds. Very few offer sites with hookups and those go first. Unless you're comfortable with dry camping AND either have a generator to recharge or know how long your batteries last, you'll be better off somewhere with, at the least, electric hookup.
Grand Canyon, not sure how fast they sell out. We stayed there once in '05 but we always make reservations months in advance. They do have a 'Trailer Village' concessionaire campground that has hookups as well as one non concessionaire 'dry camping' campground.
www.visitgrandcanyon.com/trailer-village-rv-park
We've been RVing (truck and trailer) for +20 years and for us it's the only way to go. Nothing like waking up in your own bed 3000 miles from home! We did a cross country trip to the Smokies and Disney World and back (6000 miles, 45 days) and it was absolutely wonderful. But there are drawbacks and considerations. Sight-seeing is more difficult, parking can be next to impossible so you have to think about transportation as well as camping. Certain roads/routes look breathtakingly beautiful but are not RV friendly. The TripAdvisor forums can be a great help. We've gotten good help there on towing our trailer, parking availability, good routes for large vehicles and often 'consult' there when we're headed to an unfamiliar area. The area RV experts are really good. They'd much rather you know ahead of time before you find yourself in a bad situation.
Also, remember that the US is HUGE so be sure you look at mapping/road trip websites to calculate distances and routes. And many states have lower speed limits for RVs plus you must drive much slower than the posted speed in the mountains or twisty roads. For a good 'rule of thumb' to determine how long it will take you to get from A to B in an RV, calculate your speed at 55 miles per hour 'flatland' driving. If you are doing any mountain or 'twisty' driving calculate your driving speed at around 45 mph. So a 100 mile drive that you think will take you 90 min will actually take you around 2 hours (without stops).
Happy to answer any questions you have.