Check "Zion River Resort" in Virgin UT, or "Willow Wind" in Hurricane. Both very nice parks.
After seeing Zions, drive through the tunnel and go to Bryce NP. In my estimation it is even more spectacular. Up by Cedar City is a National monument called "Cedar Breaks". It is similar but much smaller than Bryce, but worth seeing. Be warned, steep winding road, but there are RV's that drive it and there is a campground there as well. North and west of St. George is "Snow Canyon state park", worthy of a few hours and south of St. George is the "Virgin River Gorge", one of the last sections of Interstate finished in the US, and after seeing it you'll know why.
Utah is an amazingly beautiful state, with the other three NP's and many Nat'l monuments well worth the time.