We live in Anacortes, which is a really nice place, with ferries to the other Islands in the San Juan chain. It's just about 100 miles from YVR airport, along SR-20 from I-5 in Burlington. It would be a good distance if you want to make an afternoon departure the first day. There's a very good State Park (Deception Pass SP) to the south, just across on the north end of Whidbey Island.
If you are planning to visit the Seattle/Everett area (museums, Boeing factory tour, etc,) you may prefer to keep on I-5 rather than making the detour to Anacortes. Alternatively, you could head south on Whidbey and either take the ferry from Coupeville to Port Townsend and do the Olympic Peninsula or the one from Clinton, at the southern end of Whidbey, across to Mukilteo. The ferry terminal there is just a couple of miles from the Boeing Tour Center. You can continue south on I-5 from there. Be aware that the ferries aren't cheap for motor-homes.
DW and I are both ex-pat Brits, originally from Leyland in Lancashire, but long past the "young family" stage. We're at the stage of having adult grandchildren (and a couple of younger ones).
We don't have our MH any more and hadn't used it at all last season. so our recommendations will be a bit out of date. Any questions, just send a PM.
Frank Damp -Anacortes, WA,(DW- Eileen)
ex-pat Brits (1968) and now ex-RVers, as of 08 Dec 14.