Trishy34, people will want to know what month you will be traveling. That could make a big difference on routes. But you will no doubt get a lot of information, options and suggestions here, so stand by!

Wow. Lucky you! That is gorgeous country.

We live in Colorado, and can recommend places here, with info on time of year. You will get overloaded with awesome ideas!

To start, you could check fodor's books, of course.

I don't think you will save any money using an RV and paying for campsites compared with renting a car and staying in motels or National Park lodging if you are lucky enough to get a reservation.
You mentioned family. Do you have a child (children with you)?
The Fodor's guidebooks are a great place to start planning.
Don't forget to include at least 1 southern Utah National Park in between Arizona and Colorado. Arches is great.

Yes the Fodors guidebooks are great.

Depending on the date of your trip, you may find Colorado and Arizona are not a good combination. Sometimes when it's great weather in Colorado, not so in Arizona, or the other way around.

Since you've been to Arizona twice you could consider Colorado and Wyoming, or Colorado and Utah. For that you'd want to be here from May through October, more or less. All those states are loaded with fantastic and varied sites.

Have fun planning.

I would be tempted to stick with just Colorado(it sounds like you've done some in Arizona already).

Start out in Denver, head south to Colorado Springs and Pikes Peak.
Then to Great Sand Dunes
Next would be to Mesa Verde and Durango area.
Take Million Dollar Hwy and head towards Black Canyon of the Gunnison
From there over to Rocky Mountain Park Estes Park
Then back to Denver or you could include a few days at a Ski Resort for summer activities. Somewhere like Breckenridge or Winter Park. Depending on where that was located, you might want to do that before Rocky Mountains.

Great Sand Dunes is best the last of May or first of June.
Rocky Mountains is better the last part of June or even into July or August. Mesa Verde isn't fully open until the last weekend of May.

You could even cut over to Arches National Park/Moab for 2 or 3 nights.

New Mexico, Colorado and Utah. Rather than an RV, consider camping. Outfitting for car camping can be done for about $300 at stores like Target, K-Mart, Sports Authority, etc. Donate the equipment to Goodwill at the end of the trip.

To whet your appetite:

http://www.flickr.com/photos/mksfca/sets/72157622636845987/

http://www.flickr.com/photos/mksfca/sets/72157623176227912/

http://www.flickr.com/photos/mksfca/sets/72157622984070940/

For RV specific travel, a good forum can be found at Trailer Life. Scroll down to the board "RV Parks, National Parks, State Campgrounds,and More" and also the board "Roads and Routes."

forums.trailerlife.com

This guidebook might be a good addition to your reading materials:

http://www.thesavvytraveller.com/agraphics/insights/series/michelin/green_guides/americas/united_states/states_regions/west_475h.jpg