Where in southern OR are you? My preference would be to get over to Hwy-101 as soon as practical (I dislike i-5). North of Eugene take Hwy-146 to Florence and Hwy-101. If you are above Cottage Grove take Hwy-38 through Drain to Reedsport and Hwy-101. Just south of Roseburg take the road through Dillard to the Coos Bay area connection to Hwy-101. I have done all of these with my 40' 5th wheel.
Next opportunity is Hwy-199 out of Grants Pass. After that you are in CA and Hwy-299 at Redding is the 1st chance to get over to Hwy-101.
I would consider going around San Francisco and not driving Hwy-101 through there. Hwt-101 goes right through S.F. and has heavy traffic. I have done with the RV but city driving doesn't bother me that much.
I love Hwy-101 from WA to CA.