Idaho 75 from Challis to Sun Valley

We lived in Challis for 20 years and have a home in Stanley. I can't think of anything on the route that would give you a problem if you go slowly enough. Most of the route from Stanley to Sun Valley is straight two lane. Galena Summit is 9,000', but Stanley is already at 6,300', so the climb isn't as bad as it sounds. There are a couple of tighter turns over the top, but nothing that should stop you. Not going that way would mean you would miss out on some of the most spectacular scenery in Idaho.

Galena summit has some very tight switchbacks. I would be concerned when towing a toad in that it is possible the toad could go to steering lock in a sharp turn.

The road from Challis to Stanley is a two lane mountain road that follows a river which has many curves. Not a problem but can be slow and requires close attention in the curves.

You will have to go over Galena summit which does require going up a 7% grade and climb about 1500 feet.

It is not all down hill from Challis to Sun Valley. If fact it is all up hill to the top to Galena Summit then a 7% down hill drop of about 1500 feet to Sun Valley.

In Idaho going North along a river often is down hill and going South is often up hill. Many of Idaho's rivers flow North. The Salmon and Snake are two that do this.

The drive is definitely o.k. for RVers. You'll see many as you drive. You'll just be taking it slow. There are no issues for the road. From Challis to Sun Valley you will be going down, not up.

I hope you're planning on some time in Stanley and the Sawtooths.

Stanley is high, so the total climb to the south isn't as big as 9000ft altitude sounds.

As you said, the climb to Galena Summit is the biggest issue on ID 75, but it's easily doable with your MH. The grade is not too steep (7% max) and the road is in good shape.

Here is the Idaho Dept. of Transportation link for Galena Summit.