well now i will chime in, first of all ppg does not recomend soda blasting, will not warranty paint if this has been done.
good for me since i own media blasting equipment. no plastic media will not remove rust, i apon customer request roll the car out side and sand blast around window and other surface rust areas. metal that has been media blasted will not flash rust i have parts in my shop that have beeen blasted for years no rust. media will expose the areas that you need to replace, giving you time to do that before shooting you epoxy primer. but before you prime you must scuff the metal surfaces, i use a da with 180 real quick job just to give primer something to stick to. as far as cemical dip how in the world do you get primer in all the nooks and crannys unless they can did the whole car in primer?