The Washington State Rally is being held in Lynden (north of Seattle) again this year on September 11th-14th. The Whatcom County fairgrounds are first rate facilities both for RV's and getting together. There's a dealer sponsored golf tournament again this year along with an arts and crafts competition.
Many folks arrive a day or two early as there are many things to do in the area.
Go to the Wash-I-Bagos
state WIT chapter website under the Rallies link for more details and the registration form.