G'morning from South Dakota. Wtih regard to your inquiry about "Going to the sun road (being) ok for motorhomes?.....NO, it is not a route for motorhomes. While staying over in West Glacier, do take your tow car up and back on Road to the Sun, it's a great little tour, but DO NOT take your rig. I think the length limit is something like 19 ft. or 21 ft.
When you do leave West Glacier after touring the park a few days, take Hyw. #2 around the Southern margin of Glacier Park over to the town of Browning, then head South toward your West Yellowstone destination.
Steve & Lynette
2014 Newmar 3103 BAYSTAR/Triton V10 w. Banks/05 Honda Element toad