When you sand blast sheet metal its not the heat that warps it it is the peening effect of the sand. The SM 'grows' but is locked in place by the bends and welds. Even if it looks ok you still may have a oil can or soft spot. The grit size,air presure and angle have alot to do with it.
Unless this is a work truck and you are not real fussy about the sheet metal work I still say it is not a good idea.
