This time of the year camping spots generally not a problem. If one place is full the next won't be.
With that in mind you want to look at other attractions and not worry about camping. One source of information is here.
There's many things to see and do along the Oregon, Washington, and California coast. Since you only plan on traveling 200 to 250 miles per day there's lots of time to take in the sights.
Some areas in Oregon to consider spending some time.
Fort Stevens State Park. Visit the old fort.
Seaside. Take a walk on the board walk.
Tillamook. Visit the cheese factory.
Pacific City. check out the beach where the dories launch.
Depot Bay. Watchs the boats navagate the narrow channel under the bridge.
Newport. The aquarium. This a must see.
Stop at some of the waysides for views of crashing waves and shore birds.
The attractions are many. There's only two of the above have fees associated with them. Ft. Stevens and the New Port Aquarium (I believe it's called the Oregon Aquarium)
There's nothing wrong with any of the state, federal, and county parks as a place to stay.