well with the topper id start by blowing all the loose stuff off with either an air compressor or power washer. im assuming you dont have da sander? so on the small spots like on the pillar and bedside feather out the spots with either 600 or 800 grit wetsanding. the topper since its alot bigger area maybe start with 400 wet then work your way to at least 600. if u plan on priming then finishing it 400 will be fine but if you want to seal or go straight to paint the at least 600 preferably 800. i dont know how nice of a truck it is but i know i wouldnt use rattle can anything on the exterior. if you dont have the tools such as compressor, spray guns you probly be best of getting it as ready as you can and trying to get someone to spray it for you. if any of this doesnt make sense just ask!