Have you thought of reinforcing the JB Weld with some fiberglass tape? Apply some Weld, put a strip of tape on and rub it in so that the Weld works its way into the weave and then rub another coat of Weld over it. Use a plastic baggie as a glove...
I don't know if that will screw up the expansion/contraction of the rest of the cooker and cause more cracks elsewhere, though.
The drilling the hole at the end of the crack to stop propagation is a really good, really old trick. Do you want to drill all the way through to stop the crack and then fill and touch up the paint on the outside at this point? Hope someone else has tried it on something like your cooker and can give you some first hand advice...
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