The answer may depend on how you want to preserve it and how close you want to stay to an unmolested truck if that’s what you intend. You can spray oil/wax mix on it to , pulling the frame, sandblasting the surface rust and using any number of rust preventative products on it to - powder coating. There are two stage and single stage enamel paints, to urethane products such as POR15 or Chassis Saver products. Lots of options. You can brush or spray these products but removing the surface rust is key for the product to adhere.
This is a very broad answer and searching this site and the internet will bring to light these options and help you decide how you want to proceed.
Warning - you may find that once you start you will want to fix this, do that, and next thing you know you are way into a bigger project than originally intended. It happens to most of us at one time or another. Recognizing project creep is the first step toward recovery. 😉
Last edited by tom moore; 03/18/2019 10:27 PM.
