Ok, well I mixed holdtight in a 55 gallon drum 100:1, raised the drum on a forklift to create some head pressure in the supply hose, hooked that up to a pressure washer and washed down the body and parts. Worked great. I could do a hole car with about 30 gallons.
Fortunately I can skip this step in the future since my media blasting guy can remove paint off fiberglass and leave just as smooth as soda buy using fine crushed glass. I thought it would be too harsh, but he proved me wrong.