Welcome back, it has been awhile!!! Not sure what to tell you on the blasting, it's the heat from blasting that warps things.... I haven't done my own blasting for years, but never had any trouble with just plain old silica sand on the heavy metal of the older cars and trucks... Can't say my technique was the reason, but I never left the nozzle aimed at one area for too long, or had the nozzle too close to the metal, and always shot at an angle to the metal and not straight on. Took a bit longer, but no warpage problem on the older stuff....