Stu,
Do you have specific reasons for visiting the specific cities on your route. The route seems to be sort of convoluted,e.g., Portland to Lincoln City, back to Corvallis, and then back to the coast. You end you crossing the Coast Range twice. Not a big deal, but the routes are often busy and once is usually enough for most folks.
There are some better routes (scenery and camping) if all those cities are not on your "must" list.
In my limited experience with wild camping (I only do it out of necessity, and I'm not stealthy about it) in WA, as long as the timbered tracts are not posted "No Trespassing", I've not had a problem. However, because of all the wildfire activity going on, landowners might be more sensitive. A slight modification of your route will put you near WA and OR state parks that have Hiker/biker sites that are inexpensive, and have showers.
Doug