I plugged Custer to Colter Bay into Google Maps and the route you listed comes up as 475 miles. I know that there is a KOA at Douglas and a couple of campgrounds in Casper. We have used
Sleeping Bear RV Park in Lander a few times. Lander is 356 miles from Custer and adds just 22 miles to the entire trip length to Colter Bay. If you go to Lander, consider a quick visit to
Sinks Canyon State Park.We have done the drive over the Togwotee Pass a number of times, most recently last June. Beyond Dubois it's a gradual climb to the top of the pass an a somewhat steeper descent going down the west side. Lots of beautiful scenery all the way and great views of the Tetons on the west side.
Enjoy your trip!
