I go this way every year. Stay on I90 to the Cardwell Jct just past Whitehall, MT. Exit at Cardwell onto Hwy 359. Stay on 359 to the Jct with Hwy 287 & take 287. Goes past Harrison Lake & through Ennis, MT a unique little burg. Stay on 287 south out of Ennis to the jct with Hwy 87 and stay left on 287 to jct 191/287. Stay right on 287 to West Yellowstone. I take this route every year in my coach & toad to visit the park.
2008 Monaco Camelot 40PDQ, 4 slides, 2016 Dodge Ram 1500 Hemi Quadcab 4x4. Blue Ox, Garmin 760 LRM GPS, Doran Pressure pro on all 10, M&G Brake, 50 amp SurgeGuard, FMCA, Coachnet.