Mainly all I do is clean the truck well, use a wire wheel to knock off any loose flaky rust and then apply the POR15 by hand with a brush. It actually bonds better to what the manufacturer refers to as "seasoned metal and rust" so you don't want to remove all the rust, etc. If the metal isn't already rusted, etc, you don't want to use POR15 because it won't stick well and will flake off. On trucks like the white one in the shop now, I am only hitting the rear differential housing, axles, tie rods and spindles with the POR15 and coating everything else with
Amsoil MPHD heavy duty metal protector.