Mid October is a perfect time to visit/camp in the Great Northwet! generally the rains don't start until November and a sunny 70 degree day is very possible. I live on the Eastside of Seattle and I avoid going into the city at all costs. I'm retired so I have that luxury. There is a lot to see and experience on both sides of the mountains (Cascades). Generally we camp on the Westside but avoid travel during rush hour which is between 6Am and 11AM and again from 1PM to about 7PM. Fridays are always bad to try to leave especially on 405 and I5 around Tacoma and again JBLM.
On the positive side our coast is unlike many you have seen. There are sandy beaches you can drive on as well as rocky craggy beaches that can only be accessed on foot. October may bring a storm in which makes beach combing interesting. There are beautiful sights around the rain forest on the Olympic Peninsula including Heart of the Hills and Hurricane Ridge. There are many State Parks along the Puget Sound that give access to Hood Canal and the scenic Olympic Mountains.
I too recommend the North Cascades Highway for a trip across the Cascade Mountains. A favorite National Campground is Colonial Creek on the banks of the amazingly beautiful Lake Diablo. The lake is the most unusual shade of green. Be warned there are no hook ups there and the North Cascades Highway will close for the winter. Further south is Highway 2 which is a beautiful drive over Steven's Pass and takes you to the enchanting Bavarian town of Leavenworth. Blewett Pass and Interstate 90 will also carry you over the Cascades. There is a beautiful campground just East of Snoqualamie Pass called Lake Easton.
There are also many sights to see along the Columbia River. I can't remember the name of it but there is a State Parks campground at Vantage that has many great views from your site of the river valley.
The best part is when you are travelling because most of the seasonal travelers have winterized their RVs and have to stay near home because the kids are in school.
Our state is a beautiful place that has mountains, lakes large and small, an amazing desert, and a gorgeous coastline with ocean beaches that generally have few folks on them. If you like to hike, there are so many options your head will spin. C'mon up, enjoy yourself but don't tell anyone.