When west bound, after you crest the summit, don't allow your RV to get too fast. there is a 5 mile 5% grade coming off the pass, then a short climb into Rainey pass then 7 miles of 4 % off Rainey.
When east bound, it's one long down grade off the pass, it's 6% for about 2 miles, then a sweeping switch back, then its 7-8 miles of 6% into early winters. then it is over really nice ride from there into Winthrop.
Just remember there is 87 miles of no services between Mazama and Marble Mount. don't leave either with out a full tank.
West bound we usually fuel up at Twisp.(when needed) and west bound we fuel up at the reservation on 20 east of Anacorties. and again in South Dakota :)
It's a solid 5 hour drive Burlington to Okanogan.