There are two things you need to know about Seattle to survive:
1) Everyone wears plaid shirts and grunge music is played on every street corner. Wear plead to blend in, but a tin foil hat to keep Nirvana out.
2) Approximately 80% of Seattle is covered by Kpro's DNA.
Seriously though BelXavier had a solid idea. Take a tent and your sleeping bags and find a place to camp. If it is state land there will be a small fee if any.to use a campground. If you don't like the idea of roughing it but are not opposed to camping out, check out a KOA camp site. They are basically private campgrounds you can rent and the often have amenities such as water/power, showers, pools, ect.. Don't know what restrictions they have but it might be worth checking out. KOA-Seattle