Seattle RV parks
The KOA on 212th St. is your best bet. It is midway between I-5 and Hyw. 167 on the south side of the street. It is marked on the exit off of I-5.
It is an old KOA but it has been improved the last several years because of new owners. That is our first US stop when coming south from Alaska.
Seattle is one of the poorest places to find a RV park. There are very few and some are full of real old units that have been parked for years.
The park on I-90 east just east of I-405 is so tight that you almost have to grease the sides of your unit to get it into a space.
Happy camping.