Visit the Maritime Museum in Astoria - excellent for all ages. Then take the $2 riverfront trolley ride and the volunteers will tell you about the waterfront history. Recommend Rogue Brewery and there is one at the east end of the trolley. Stay at Ft Stevens if you can but otherwise visit the coast through the park.
With this start the entire coast is ahead of you. Almost all of the turnouts are on the ocean side on a curve. Easier access than north bound where you cross the often blind traffic.
Go as far south as you want and don't miss the CA redwoods. Then backtrack and take 199 to Crater Lake. 299 is more of a challenge so read about it first.
Note for others: 199 in CA is prohibited for MHs over 40'.
There is no reason to leave your rig behind, all of the above roads are good 2 lane roads.