Originally Posted by Bubwheat
Take I-10 to San Bernardino, I-15 thru Barstow, and then 395 North to Susanville, then 299 over to Redding, where you can take 1-5 North to Seattle.
Good combo of speed and scenic, and some very nice campgrounds along 395.
Were you to use this route, pick up 395 between Cajon Pass and Victorville.
My recommendation would be, once you get to 395, take it to 58 to 99. Stay on 99 until the Manteca area, where you should take 120 to 5. (Much simpler to get thru Sacramento this way.). 5 takes you to Seattle. Here are the parks I've used along the way. All are more than acceptable, most are excellent. Saddle Mountain, Desert Willow, Orange Grove, Bakersfield RV Resort, Flag City, Premier in Redding, Mountain Gate, also in Redding, Seven Feathers (I haven't actually been to yet but just check it's reviews!) and Brookhollow in Kelso. This route maximizes freeway. 395, once the fishing season starts along the Eastern Sierra, can be pretty challenging for RV parks with full hook-ups.