I worked CHP in Red Bluff for four years. DO NOT take SR 36 From 101 to Red Bluff. Take 299. 36 to to 101 is very crooked, narrow and not RV Friendly. We only patrolled about 10 miles west of town. Very remote.
36 to Susanville is good road, very scenic, but again remote. Crooked for a few miles west of Mineral, otherwise very good road with little traffic.
I'd gas up in Red Bluff and you'd have no problems.
Depending when you go east over the Cascades, there can be significant snow. Some roads in Lassen NP, just north of Mineral get 60+ FEET of snow with 30+ on the ground.
They try to open north/south highway by 4th of July and consider it a long summer if it is still open at Halloween.
SR 36 gets lots of snow but rarely closes and is well plowed.