After the coast of OR, you'll be disappointed in the northern coast of WA. After Grays Harbor/North Bay I would not bother and head to Olympic NP and the area around Sequim. From there I'd take the Port Townsend/Keystone ferry over to 20 and north to Oak Harbor, Deception Pass, and Anacortes. Washington Park near the ferry to CA is one of the prettiest CG and scenic loops anywhere.
*In looking where Ephrata, WA is, I would not even bother with the southern Pacific coast of WA and instead head straight to Whidbey Island. I might even leave the MH at Anacortes and take the toad to Victory and spend several days there staying in motels as that will be less expensive than taking your 34' RV. It would help if you put your 2000 National Seabreeze in your Sig. If no toad then I would do the loop to Victory and then the ferry to Port Angles and Olympic NP.