Not the best time of year for in the PNW my friend. The San Juan Islands are fantastic, try to start your adventure their after first experiencing BC. From the SJ Islands take a float plane to South Lake Union ( Kenmore Air). However you get to the Seattle area, I would suggest making your way to Whidbey Island and camp here - http://www.parks.wa.gov/507/Fort-Ebey
. Not sure when the park closes for the winter but it's my families favorite local spot for camping. While on Whidbey be sure to check out this - http://www.parks.wa.gov/505/Fort-Casey
. Sitting on the anti aircraft gun rescued from the Philippines and seeing the huge holes blown through the 1" + thick steel plate that protected the gunner as well as the divits in the barrel will make the hair on your neck stand up. The massive guns at the wall are really cool also. Click this for photos. https://www.google.com/search?q=fort+ca ... d=0CB0QsAQ
MT ST Helens would also be a cool place to visit, weather could be an issue though. There is a great visitors center their sponsored by Weyerhaeuser, another great PNW company. Speaking of great PNW companies, you have to check out Boeing in Everett. They give plant tours, you will get to go through the largest (by volume) building in the world. Just south of that is Paul Allen's flying museum, if your a WW2 buff. Best collection in the world of aircraft from that era that still fly. You will be escorted around the museum by your own personnel WW2 historian.