Welcome aboard the RoadTrip America Forums!

With a RoadTrip of this magnitude, it is usually best to establish a modestly precise outline of where you'll be when, a rough itinerary, so that you can start filling in details for various sections of it one at a time. You've already got a decent start with fairly certain ideas of what you want to see, a pace that will allow you to travel in comfort, and an overall time budget. The next step is to work out blocks of time for each portion: Utah, Yellowstone, South Dakota, Houston, and getting between them all. A quick check of your routing indicates that you'll need about eleven to twelve days of driving at your preferred pace of only six hours a day. That doesn't leave a whole lot of time for each of the areas you want to visit, maybe three days or so each, but at least you can start your planning with those timeframes in mind.

With all that in mind, let's try to answer some of your current questions. For Red Rock Country, I think you'd be hard pressed to do better than Zion and Arches, so those are the ones I'd recommend. The other Utah destination I'd suggest would be Dinosaur National Monument. All national parks have roads and parking lots that can handle RVs, as well as campsites. But the campsites fill up early, figure out your itinerary and start making reservations as soon as possible. The other thing to know about our national parks and monuments is a program called Junior Rangers. This is perfect for children of your grandsons' ages. Be sure to sign them up at each park you come to. Not only will they get activities to help them make the most of their time in the parks, but upon completion of those activities they'll get some neat (free!) souvenirs,

Between Yellowstone and southwestern South Dakota, most mapping software will suggest US-14, but I think you might be better off by leaving Yellowstone to the north through Livingston. US-14 is steep and twisty in places and besides, I-90 will take you past the Little Bighorn Battlefield. In addition to the South Dakota sites you've listed, also check out Devils Tower in nearby Wyoming, the Crazy Horse Memorial, and Wind and Jewel Caves for a little variety.

And don't overlook some great sites in between your (so far) listed destinations. For example, give thought to the sites along the old Oregon Trail in Nebraska (US-30 along the Platte River), sites in Texas such as the Alamo and LBJ Ranch, and sites in Baja Arizona such as Tombstone, Kartchner Caverns and the Pima Air and Space Museum.

So the next steps are up to you, choosing a direction of travel and more importantly how to apportion your time amongst all the possibilities. Once you've got that level of planning we can offer some further thoughts that might be of help. It's what we're here for.

AZBuck