We did that same route last spring: Newport, WA (Old American CG) to W. Glacier on US-2. It is 2 lane most of the way. Good road. Very scenic. You won’t regret it. No problem.
IF you ever need a good CG on any west trips to or from Rapid, “Jim & Mary’ CG” at exit 96 on I-90 on the west edge of Missoula. Very clean, well-maintained, nice garden displays with many pull-throughs if you’re staying only one night. Discovered it on our Yellowstone trip in ‘15 and have used it ever since.
2011 Chevy 2500 Duramax diesel
2019 Timber Ridge 24RLS (Outdoors RV)
Go Cougs!