Soda blasting the outside is obviously a better route. I'm not saying sand can't or hasn't been used before, but it definitely is more abrasive and generates more heat. I blasted my firewall but stayed about 3 feet away and was using a small pot blaster. It took forever, but kept the heat down and didn't warp anything.
My only word of advice is make sure they stay off the panels as far as they can. Let us know how it goes.
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