That truck's lookin' good. You may need to get placard before they let you drive away:
http://app.leg.wa.gov/RCW/default.aspx?cite=46.37.467
And it looks like you don't need to get fuel from a specific source such as a gas station since there is a special annual fee instead of tax:
http://app.leg.wa.gov/RCW/default.aspx?cite=82.38.075
I was wondering if the tank needs re-certification, but maybe not since it's permanently mounted.