I always spray on a coat of PPG's DPLF Epoxy sealer on any raw /blasted metal to keep it from surface rusting !
Just handling the raw steel with your hands will start to form rust , as your hands have moisture and the salt from this moisture attach to the raw metal starting it to rust . I usually wear those disposable blue rubber shop gloves when handling the raw metal too .
All it takes is a 3M 3" scotch brite abrasive pad on a die grinder to remove the epoxy primer for the repair .

Sure beats wasting money watching your panel surface rust again after just having it sand blasted !

even a light coat of rattle can rustoleum gray or red oxide primer is better then leaving it raw metal
Need to protect it as must as possible because as soon as the air hits it , it starts to rust .