I found when trying this with the kids years ago, sidewalk did not work well, and it is a pain to try to clean up. Foil worked better, and a car hood with foil worked best. We also learned if your AC goes off in summer, and you are on vacation for a few days so no one notices, bad things happen. With daily highs running between 110 and 120, jars of food will explode in your pantry, and cook on the walls and ceiling.
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