If you don't have a title, how do you get a license plate for it? I would be concerned it may have been stolen, or the title lost.
I believe in Washington state, if you are not the legal owner, the state will issue a registration certificate but not a title for 2 or 3 years to ascertain it is not stolen.
Washington also requires plates for most anything towable.
2015 White Hawk 20MRB (It's last year)
2011 F150 Non EcoBoost (5.0)
Reese Steadi Flex WDH