Mike Buzzeo definitely knew how to cover a plane, and the wing he was working on was not a flimsy frame. Even if you cover both sides first, you can not heat both sides at once when you shrink it, thus you have to progress around the wing in an orderly manner, which Mike does by starting with the panels closes to the wing root first. The possibility of warping exists no matter how you proceed if you shrink one area too tightly before the entire wing has been shrunk to some degree.