In reply to Greenbanks:
How long are you going to stay?
Vegas is far away from yosemite and monument valley. It is also a good 2-3 hours to Zion or the grand canyon. not much of a base if you intend to return every night.
Personally I would road trip. There are plenty of campsites, an RV and tent would be perfect. You could then drive from national park to national park and expereince more time at a particular place.
http://www.cruiseamerica.com/rent/our_vehicles/standard_rv.aspx
The US is set up for vehicles like this one.