From AAA for Washington:

The certificate of ownership for a manufactured home may be eliminated or not issued when the manufactured home is registered as real property.

When the certificate of ownership is eliminated or not issued, the application for license must be recorded in the county property records of the county where the real property to which the home is affixed is located. All license fees and taxes applicable to the mobile home as a vehicle must be collected prior to recording the ownership with the county auditor.

When the ownership of a mobile home is transferred and the new owner applies for a new certificate of ownership, the DOL or county auditor must notify the county assessor of the county where the mobile home is located of the change in ownership including the name and address of the new owner and the name of the former owner. A certificate of ownership for a mobile home will not be transferred or issued until the DOL has verified that any property taxes due on the mobile home have been paid.

In order to transfer ownership of a mobile home, all registered owners of record must sign the title certificate releasing their ownership.

Any person moving a mobile home on public highways must obtain a special permit from the DOT and local authorities. A special permit will not be valid until the county treasurer of the county in which the mobile home is located has endorsed or attached his certificate to the permit certifying that all property taxes on the mobile home have been satisfied.