Use a polishing machine to remove rust, and even if the paint is good, the truck will inevitably rust. I suggest you don't do a lot of useless work in the carriage. Mainly to pull corrosive goods as little as possible at ordinary times, and brush the car quickly after each pull. The derusting work before painting is very dirty, so it is understandable that you want to polish it carefully. After painting, spray bright paint or varnish again to protect the primer.