Matt
Brian is corect unless the person doing the blasting knows what he's doing the pressure of the sand along with heat builup will definatly warp panels. I have had panels done wth sand and with plastic beads both came out very well but the same guy did both and has been doing it for many years. As my Canadian brother said, it is common to have the panels primed prior to body work, make sure thay use a primer that is made to go directly on bare metal. Believe me it is a real pain to have the primer coat flake off during the prep work. The only down side to the blasting is the residual sand left in every nook and cranny. But a lot cheaper then chemicals.
Good luck.
Al

Allan S Langley B.C Canada