Painting Prep

[Houlihan17]

So in a few days im gonna spray the bottom of my truck with spray bomb with clear coat mixed in. i am wondering what grid sand paper to use and is there anything i can apply to make sure paint sticks good? Also i was thinking of painting under the wheel wells is it better to paint or is there a guard i can spray under there sorta like bed liner type deal? im most worried about rust thats why im asking these questions.

Please any info or tips will help thanks

[88K5]

It's always good to prime 1st. 600 grit for final sanding before paint is good. Rubberized undercoating for the wheelwells is a cheap but durable solution.