Ummmm….uhh…. Plan? Lol…. I’m sure it will be some combination of cut/weld/ and hammering. What could possibly go wrong? I think I’ll creat a spare one to practice on.
I'd put a small flat plate on the inside of the channel and attach it with a couple of rosette welds. That will strengthen the channel and help prevent any cracking at the weld. If you put it inside before welding the thin channels together it will also help prevent blowing thru the thin metal.
I don't have the necessary equipment or a place to keep it so for metal supplies such as that I just call my local metal supplier in the morning with my needs and pick it up after lunch. They charge by the bend, cut and material cost by weight, which is minimal for someone not outfitted for those jobs. Just the time saved for me is worth the price.