We passed through Sandpoint on the morning of September 21st on our way from Libby, Montana to Winthrop, Wa. Too bad we didn't cross paths... Looks you're in for another gooder.
Some great roads in Western Montana and Eastern Washington. I noticed you really liked 31, New Denver/Kaslo, one of my faves as well. Found a little backroad off Wa 20 at Usk to Chewelah (Flowery Trail Road I think) it was a real treat! You'll have to try it sometime.
Enjoy your trip buddy and stay safe! I'm subscribed!