We spent all last summer in the Colorado mountains. As long as you stay in the higher elevations you won't need air conditioning and it's beautiful! Gold mining history, hiking and train rides for the kids. The west side of the Rockies aren't as busy in the summer.
I prefer this site for free campgrounds because the maps make it easier -
http://freecampsites.net/usa/ This one is good too -
http://www.ultimatecampgrounds.com/uc/index.php And for private parks -
http://www.rvparkreviews.com/ If you're moving a lot your batteries will stay charged up and you'll only need commercial campgrounds to dump and fill your water tank. Have a good time!
