In reply to TonyB:
> Amazingly it's a very similar price to hire a small van that sleeps 3 and a monster van that sleeps 8.
Yes, we have found this too. It's frustrating but we end up hiring the cheapest RVs rather than a camper van. Very comfortable for camping in, but not so easy to park at the crag.
Public campgrounds usually charge per site (pitch) rather than per person so with a large group you'll get good value to partly offset the cost of rental.
Yes, it drinks a lot of fuel, but fuel prices are cheap and the tanks are large, so apart from concerns about the environment you don't notice this as much as you'd expect.
Added to this, roads and campgrounds in the US are designed for large vehicles and manoeuvring isn't as difficult as it would be in Europe.
Finally, re bears and food stored in RVs, the official advice is that this is fine, and we've never had any problems. You'll have a monster fridge in a big RV anyway!