It's kind of late here, but I have exactly the same thermometer that Peruvian has. Here is how I waterproof them.
https://www.homebrewtalk.com/showthread.php?t=590455
Might work for you guys too.
If you buy those $10 digital oven thermometers and use them in any kind of liquid the probes die very quickly. The first one I bought lasted two brews after getting dunked in the wort.
You don't need to buy a $100 thermometer to get waterproofness.
I made a short video about how to solve...