Yellowstone & Grand Teton next summer, from Colorado Springs

A little late (been getting one last camping trip in Moab), but some food for thought. When we lived in the Denver area, we'd stop somewhere in the middle, for even w/o kids, it's a long haul. One time on Casper Mountain. Several times in the Bighorn Mountains off US 14 or US 16. A couple of times near Pinedale, WY. Since you're doing a round trip, I'd suggest one route up and another back.