Best route Wyoming-Colton Bay to Grizzly in a 45 Motorhome

I agree with others that you will have no issues with the route through the Park from Colter Bay to West Yellowstone.

Just as a heads up, a few miles after the South entrance the road follows along the edge of the Lewis River Canyon for a mile or two. Going northbound, your passenger will be looking down over the edge, which could be disconcerting to a person who has a fear of heights. No saying this to discourage you, just passing along so you will know what to expect when you get there.