In reply to Bobling:
> Also we're thinking about hiring an RV - any advice/thoughts appreciated!
If you liked camping in Carolina you'll love camping in the south west!
We've rented small RVs in the US several times when our kids were young (including a 3 month road trip when they were 8 and 10) and it was always great.
Campgrounds in the most spectacular national and state parks tend to have fairly basic facilities so an RV makes it easier to enjoy these places.
Higher altitudes will also be pretty cold at Easter, so you'll probably appreciate having a warm space to retreat to in the evening. And it means you don't need to be so careful about wildlife - from bears in the sierras to rattlesnakes in the desert.
A couple of tips:
RVs described as 'small' or 'mini' on US rental sites are pretty spacious. We found the smallest (22ft) plenty big enough for a family of 4 for 3 months - anything bigger just gets harder to drive.
There are two quite different types of campgrounds in the US - commercial and public. The commercial ones are usually very developed, with lots of facilities and huge RVs. Public campgrounds include those in National and State parks, plus a vast network of National Forest campgrounds. These have more basic facilities but many are in beautiful wilderness locations, with widely spaced pitches so that you feel like you're wild camping.
I'm sure you'll have a fantastic trip whatever you decide to do - and feel free to PM if you have any more questions about RV rental.