My problem with soda, or any other soft media, it doesn't take rust off or anything tough like undercoating, there are enough bends curves and strong spots that sand will not warp the steel, it just don't happen. Sand blast, blow it off, wipe it down... bang prime it and paint it. The other issue is that sand blasting will give a bit of an etch to the steel, soda... not so much, then you should sand the steel after soda to get it to stick really good.