Looking at the Chief Joseph pass area I'm currently leaning towards sending a box to the Sula Country Store. When I get there I'll scope it out and either stay or hitch on up to Darby.
According to Google, Wisdom isn't much which leaves Salmon as an alternate to Sula/Darby.
Is there a lot of traffic on the highway? I could forego the box at Sula and just stand on whichever side of the road a car is driving down and leave Darby or Salmon up to fate.