Trident ~
If you stop and think about it the paint that is on your truck is, and has been sticking to that smooth bare metal under it for years.
All that is necessary is some light fine sanding.
If you do feel like putting some elbow grease into your prep work, do NOT use course sandpaper, use something a lot finer than course.
Or your sand marks will show through when the sun hits it just right.
Like CatDog said, the MOST important thing is CLEAN DRY surface.
If given a choice I would go with the soda-blast.
It does not heat up the metal like sand blasting does.