After I flushed mine for rust treatment, there wasn't any issue with the tank blowing up when I had to braze it. I will say though that I was a bit worried...so I put it out in our yard and hid behind a wooden bench we have back there. With a broom handle, a coat hanger and a mini torch, I dangled the flame over the gas cap area and inside the tank...nothing happened of course, but I was glad to have taken the steps to verify that. I'm sure there's a better way to do that...but it worked for me.
I wish you had a video of that to post Brassneck........