When we go to Yellowstone...been there three times....love it. I head up the I15 spend the night in Cedar City at KOA.
The next day we head north until we get to highway 89 north of Salt Lake City. Hang a right at highway 89 and overnight in Logan, UT.
Next day we leave Logan and head towards Bear Lake and into the Tetons, spend a couple of nights at Colter Bay RV Resort.
Head out from there into the south entrance of Yellowstone through the park into West Yellowstone and the Grizzly RV Park..
We have also stayed in the park at Fishing Bridge and Madison, Enjoyed Grizzly the best. Blog has pictures and route if you are interested.