Re: Blanking out windows--you really need to read this!
OR, use a little thicker sheet metal. I was going to use 16 Ga. as that is what the local dealer had in stock. I ended up using 18 ga. which was still thicker than the original sheet metal. Put it up in the winter. Has now sat out in the hot days sun and the cold evenings (high desert) without any deforming or rippling. 20 Ga. ot thinner, I would suspect, would be a different issue.
"I've never been lost, but I been mighty confused for several days"