Hwy 20 north of Idaho Falls to West Yellowstone is a good road with two climbs. One is 6 miles north of Ashton - Ashton Hill. It's 4.5 miles of a steady 6% climb. The highway levels off and then the next grade is Targhee Pass at the Idaho Montana border and although it's 1.5 miles of 4 - 6% grade, it's hardly noticeable. We've driven this route and you're MH can probably handle Ashton Hill if you're not overloaded. We've driven all the way to I-90. We haven't driven 12 to 89, but according to the Mountain West directory, between White Sulphur Springs and Neihart is King's Hill Pass - 6 - 7% for 4.5 miles and a 1/2 mile break in the grade near the top. It's a good two lane road with 45 mph curves on the north side and 40mph curves on the south side.
