This thread is not a "How to sand blast", sure there are ways you "can". This thread is about WHY sandblasting will warp sheet metal.
It is also the reason why I will say over and over until I am blue in the face, DO NOT SAND BLAST SHEET METAL PANELS. I am not speaking to everyone, as you point out YOU have done it. You took the chance, or practiced on something or whatever and can pull it off. I warn others DO NOT SAND BLAST SHEET METAL PANELS because the learning curve is VERY steep. I don't want to see some newbe ruining his car because he reads somewhere that it "can" be done.
You see, as some of these other posts say, you don't cause a "Crap, I messed up the panel I have more work to do" kind of damage. You cause a "HOLY #$^@ I RUINED THE PANEL AND HAVE TO TOSS IT IN THE GARBAGE!" kind of damage.