Three weeks is tight considering all you want to do in the Anaheim area. Disneyland it self is three days. I suggest besides bypassing Washington also bypass Oregon to save time. Oregon is not a drive through.
Head down I-5 then cut over to the 101 at northern California to Crescent City. There is a campground there called Shoreline RV campground right beside the water. Great area to walk, drive explore. Look for the Chart Room restaurant on a pier, great seafood.
Heading south on 101 traveling through Redwood state park, keep an eye out for for a stop at Trees of Mystery. Very extensive native displays, quite interesting, trails amongst the trees and gondola ride.
Eureka we stayed at the KOA, I needed the hottub and explored the area. Went on a tour boat ride and explored WW2 bunkers.
Heading for San Francisco stay on 101 as we were advised #1 is a very winding at times cliff hugger of a road best driven with out an RV. Since you want to make time it would slow you down.
In San Francisco we stayed at San Francisco RV Resort in Pacifica. It is situated on a bluff above the ocean, a bit pricey but the sunsets in the evening are worth it. Make reservations as soon as able, quite popular especially trying to get an ocean view. We stayed a week and had to move three times as didn't have a reservation. Oh did I mention the whales going by, seasonal, we where there first week of October. To get into town, Fishermans wharf a bus can be caught out front to the Bart station then a street car. This trip can take upto two hours so if not minding to drive in the traffic, drive. There is parking near the wharf. The resort has maps on how to use the transportation system and driving.
I have no further information farther south as we traveled south from Grand Forks BC, to Reno then up the coast as described.
Heading home just blow up I5 because you may have run out of time.
When heading home the Black Bear restaurant in Mt. Shasta has great burgers and baked goods.