I completed a bike tour of Mt Shasta > Dorris > Ft Klamath > Diamond Lake > Idelwyle > Elkton > Reedsport > Port Orford > Brookings > Cave Junction > Jacksonville tallying around 650 miles and 40K+ vertical feet. My tour was inspired by your Umpqua Valley scenic bikeway proposal and presentation materials.
You might be interested in some of the pictures I took. It was an excellent trip though not everything was perfect. I got caught in that bad weather from a couple weeks ago when going through Crater Lake. Susan Creek campground was full and I had to get a motel room at the Dogwood which turned out fine since I met the owner Norm who is a swell guy. Then the campground I planned over on Tyee turned out to be a boat launch and the BLM campground at Bullock was full. So, I ended up at the RV park about 8 miles east of Elkton (I think it is the Umpqua RV Park) which is owned by a great guy who bought it a year or so ago and is fixing it up. He might have saved my life since they were full too but he set me up with a tent site and gave me food.
The Umpqua Lighthouse campground is maybe the lousiest campground on the OR coast. No hot water though some longer term campers said it works sometimes and the noise from the dune motorheads goes until at least 10 pm. The hiker-biker site is decent there but the other issues would dissuade me from using it again. I would ride longer to Tugmans to get a hot shower next time though the lighthouse is nice to see and photograph.
Anyhow, I am not complaining about anything since it was a fun tour and I got to see new territory. I loved the waterfalls along the eastern portion of 138. One route change to possibly consider which maybe you did already is to use North Bank instead of staying on 138 into Roseburg. I liked Garden Valley Rd but North Bank is way more scenic. I could understand that for services and things like that, you wanted to route through Roseburg, but, Sutherlin has most of what a person needs. Something to consider.