Whatever time, especially with a RV, you have spend it in the Four Corners/Colorado Plateau region.
Do not miss Moab, Utah. The Arches and the Canyonlands National Parks are the best. The Antelope Slot Canyon, near Page AZ, needs a reservation to see and then go across Arizona to the north edge of the Grand Canyon (but not in the winter, the road to the lodge and viewpoints is closed after the snows start). Then wind your way through Zion and down to Las Vegas. Then on to Reno. You will enjoy some of the most beautiful areas of the country in the Southwest!