Originally Posted by willynilly
Dunno how well a silicone caulk is going to plug the hole....
Yeah, that's the problem. Nothing really adheres well to the plastic that these coolers are made from. Silicone won't do you much good as soon as it loses its adhesion to the wall, which doesn't take much.
I've used silicone with good results when smeared on a bulkhead fitting as an added level of waterproofing, but the one time I tried to seal a probe in a small hole in the cooler wall, it was leaking after just a couple uses.
If you wanted to install one of those weldless thermometers, you can enlarge the hole in the OUTER shell of the cooler so that you are sealing the thermometer directly against the INSIDE shell of the cooler. I did this on both my coolers when installing sight glass + thermometer probe.