Google up mail forwarders in the area you are looking for.
Be careful on where you choose...we had some friends that moved to a county that has fed, county and some other court system. She (not he) kept getting called to jury duty over about a 3 year period. They let her off twice, then on third time they said "be here". They were in MO. at the time. They came back.
Mail service. We have a P.O. box at a UPS store type thing. Each one is a franchise I think. The one we are currently with I can't wait to get away from. Previous mail forwarder was great except for its location.
And for what's it worth we'd be out of WA except for our medical insurance.
Here is some info that might help.
http://access.wa.gov/topics/living/becomeresident