OP -
Seattle has tight restrictions on AirBnB rentals due to the zero vacancy rate on reasonably-priced (if there is such a thing in Seattle) rental housing.
You might also be required to get a license of some sort.
If I were in your shoes, I would want to have everything above board and legal so nothing would go wrong while I was gone. For example, neighbors could report any non-compliant activity which could be a nightmare to deal with while you are gone.
Best of luck!