I see that you have already learned what you were after, but just to add a little...Under normal circumstances, Hwy's 26, 18, 20, 34, 126, 38, and 42 are all perfectly fine for large vehicles. They each have their own highlights and pitfalls. Personally, I like following the Umpqua River the best (Hwy 38), even though I live on 126. Enjoy your trip!
'04 GMC Sierra 2500HD, CCSB, D/A, MaxBrake, B&W Companion, Retrax Pro, AR Power Steps
2013 Rockwood 8289WS w/Diamond pkg
1969 Camaro RS/SS Convertible
Dad's old 1968 Empi Imp (recently recovered from under 21 years worth of boxes/dust)