I've had exactly the opposite - an utter failure with JB waterweld (which IS food safe). It simply flaked up after a couple uses on the high-stress opening of a cooler. It simply does not adhere much (if at all) to HDPE - as is the case for most fixes.
After much research, I came across what I considered to be probably the most effective and longterm fix. It was "welding" in some HDPE into the cracks inside the cooler. I was almost about to try it until I decided, "screw it", and bought a new cooler for ~$20.