​RE: State Parks Along The Wash-Or Coast.
Parks I have stayed in that I find no problems with include Cape
Disappointment (cam[ping near beach) on the Washington side of the mouth
the Columbia and Ft. Stevens just south of Astoria. And I have stayed at
several of the Oregon State parks along the coast and they (as most if not
all of Oregon Parks) are all good. And many State Parks along the Oregon
coast.
And that sounds like a nice trip.  You might check the calender at
wetwesties.org to see if some part of your trip puts you near to a
WetWesties gathering in time and place.