You will need to contact the Department of Motor Vehicles for the state of Washington for information on registration. If you are required to register your car in Washington, then you would likely need a Washington insurance policy with your Seattle address.
Hello, Getting car insurance can be quite complicated for foreign drivers, especially with short-term car rentals. Since you are renting the car from your host I assume that you will be living at their address.
We can help you in finding insurance! We would just need an address that you would use as the garaging address for the vehicle. If you use New Mexico or California we are licensed to operate in both states.