The laws of physics at play here..
Heating will expand (stretch) the metal,yet soft to bend.
Drawback is when it cools it will contract (or shrink) and will not be what you want when cooled.
Not doing any favours by heating it up.A risk of distorting the sheetmetal.Working the metal after it is heated/cooled can also harden it and tougher to work with.
Just more work than necessary,IMHO
With a good eye and elbow grease,test fit over and over and over till it is right.
Hope this helps.