Sorry about the heat wave! Consider heading further west instead - we generally stay cool on the north shore of the Olympic Peninsula and along the Pacific coast no matter what. Also, Whidbey Island has a few nice parks where you can camp - it should be relatively cool there in the coming week (the water effect again), and you can get there without taking a ferry.
OTOH, we're also not immune to forest fires in WA, so you need to check on whether there are any along your intended routes - e.g. we currently have one on in Olympic National Park. We also have a burn ban, so no campfires of any kind in state parks until at least September. <sigh>
Rocinante is our 2014 International Signature 27FB
(Named for John Steinbeck's camper from "Travels With Charley")