Hwy 93 out of Missoula into Idaho

We've towed all over this state and into Montana and have driven those routes. You didn't mention what you're driving or towing, but if you have adequate power to go over any of the passes in Colorado, then Lost Trail and Galena Summit won't be a problem. Lost Trail is short and winding, good and wide enough. Galena Summit is wide enough too but the climb from the north is slow and gradual. Once you get to the summit, there is a rest stop. Shortly past the summit, on the way down there are some short and narrow turns, then a gradual ride all the way into Ketchum and Sun Valley. There's a nice wide rest area at the intersection of 75 and 20. Hwy 20 all the way is good with one very short downhill and winding section after you pass the turn off to Little Camas Reservoir. Again, if you have a setup with good power and control, then none of these are a problem, to be respected for sure, but the beauty can't be missed. If you happen to be passing through the Challis area close to stopping for the night, there's a very nice RV Park between Clayton and Stanley right on the highway, Torrey's Inn. They have a web site and full hookups right on the Salmon River. Easy in and easy out. Have fun.