here's a simple one, drill a hole in the cooler, insert the weldless fitting, and insert brewmometer. is this going to screw up the cooler in some way? ruin the insulation maybe?
I've drilled a cooler for one of the Thermo-thingies for an HLT. I still haven't gotten the thing to stop dripping. I didn't bother on my mashtun. I just measure temp at the beginning and end of mash. My 10 gal Rubbermaid cooler holds to a degree or two over an hour.