JB Weld?
I had a tank on a ZX1000R start leaking, badly, on a trip to Washington DC one day. I got a ride to a auto parts store, and got JB Weld, the quick version. The seam at the bottom had a good long section that was bad, very bad, with a gap of almost 1/8 inch in a couple spots after cleaning the area to get it ready to patch. The area that needed patched was about 1 1/2 inches long.
I patched it, waited 45 minutes, filled it with the gas gan I also bought, then rode to the gas station and filled it the rest of the way. I continued on to DC, spent the night, then rode back to Pittsburgh the next day.
That patch lasted 2 years before I finally found a used tank on Ebay. It had just begin to break down after two years.