You might want to read this review. It is a few years old but still very good. http://www.rvcruzer.com/ystoneindex.php
Two years ago we went to Red Lodge so we could go over the Beartooth Hwy but it was closed for one day due to a snow storm. It was the start of the labor day weekend. We went south from Red Lodge to Cody and then up the Chief Joseph Hwy to Cooke City and over to Gardiner. Very pretty drive. Be sure to see the Buffalo Bill Museum in Cody. Later we went up the Beartooth Hwy to the "Top of the world store". before returning to Gardiner. The northeast entrance to Yellowstone is where you will see the most animals.