His name was Accord786
And you don't really need to have a way to bend them. If you use 20 gauge it's pretty thin metal that you can easily bend. You should be able to kind of "fold" them into shape once you put the corners into place. If you have someone help you with it and hold the corners where it fits nicely you should be able to do a couple tack welds towards the top to hold it. Then make the adjustments as you finish welding down the sides. I haven't done it yet, but it should work out.
Fortunately, I bought an English wheel. They're pretty fun to mess with. I used it with the 16 gauge metal that I used on my wheel well tubs. The thicker metal was harder to bend by hand so the English wheel was nice to have to get into th basic shape. But even then I was still able to do a couple tack welds on one side and move it around to make it fit correctly.