Have fun...I plan for us to do similar 20 years down the road..
Only in the opposite direction...what national park are you visiting?
olympia NP
The Ferry from Victoria BC crosses to Port Angeles WA. There is a company there that has a Budget rent a car agency, a hotel and a bus line.
You take the ferry and stay in their hotel right at the station, rent a car to visit the park for several days and then return to their hotel. The next morning their bus takes you to the Amtrack station in seattle
As experienced auto/rv travelers, it is a little disconcerting to rely on others and public transit......but that is the adventure