I would not use either, after my experience I would use untempered Masonic. I believe that would flex enough to not break when installed.
All that info is on the company website, or give them a call.
You can put them however you want, remember you need some structure as this is a ceiling, they recommend you buy two. You are thinking width right? Length beyond what they claim will result in a flat spot in the middle.
Yes call the company, they will fill you in on any customization you want. They do a lot.
It can be cut or even overlapped for a shorter opening.
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