This id going to be a tough one. My only thought would be to get a scrap of stainless, maybe 4"x4", and give it a little roll to contour to the pot. Rivet each corner, and then use some JB Weld on the outside of the pot to seal it.
Edit : Wait, you said cooler.....so I guess this means plastic, so use a scrap of plastic in place of the SS.