I just tried trimming one of my door openings a few hours ago. I was really scared of this because I've never really had any metalworking experience. I can't believe how nice it turned out!
I used 1/2" x 1/2" x 1/16" angle from Menards, without trimming a leg. I drilled and countersunk screw holes before I annealed it. I used a candle to put the soot on and a regular propane torch. At first I had the angle sitting horizontally on a couple of bricks. As I got near the middle it just kind of sagged under its own weight. Then I tried standing it up, but then it bent and twisted in the other direction. By the time I was done, it looked like it had been laying in the middle of the interstate for a couple of hours.
I figured I didn't have anything to lose so I put in the first screw, and just started bopping it with a rubber mallet, and putting in more screws as I went along. I was amazed how it straightened out and went around the curves like I knew what I was doing. Did I say it turned out great?
After I get the other side done, and trim the doors, I'll take it all off and put clear silicone caulk underneath and put it all back on.
Al.