For what it's worth.
My experience is that many people from UK/EU haven't a clue how big the USA is or how long it takes to see most things. I have owned an RV for over 20 years and there are still a long list of things I have yet to see. RV is a great way of seeing the USA but 500 miles eats up most of your day and it would still take 6 days to go from west/east cost.
Further - six people plus a driver is a TIGHT fight for even a BIG rv which aren't typically available through std RV rental sites.
IMO - consider renting a std Class A/C rig - drive it yourself - confine your trip to one region of the USA. I am from the West Coast and the last 2 week RV trip I had included Vegas, Bryce Canyon, Grand Canyon, Monument Valley, Dinosaur National Monument, Rushmore, Yellowstone. Could have spent a few more days in each spot if I had the time.
Long story short ... RVing is an adventure -- follow your nose -- forget the hired guide.
PS.... RV Parks and campgrounds are plentiful throughout the USA - especially in tourist spots .. no need to worry about illegal camping.
