They have an extra long thermowell that will work. It comes with the ftss not sure if they will sell separately but ask.
I bought the standard brew bucket, then decided I wanted to add a thermowell in the top of the lid. The standard lid had one hole so I put in a 90 degree elbow for a BO tube.
Without doing much research, I ordered their thermowell and the 17mm hole bit to make a precise hole. When the order arrived, the thermowell was way too short to reach a normal level of 5.5G wort from above. I contacted them and they do have an extra long thermowell that would reach deep enough but this only comes with the FTSs kit. They don't sell these components separately since they only sell them as a package. I respect their position.
This forced me to drill into the side of the bucket similar to the way their brew master version is pre-drilled. I think their intention with that is to use an LCD thermometer they include, or simply use an ATC probe as I intended.
So, with all that said, I drilled the side successfully and cleanly. For what it's worth, I have not had one single drop to leak. I am satisfied with the way it all turned out.
Brewers Hardware has a selection of ss thermowell's, some of which have weld less bulkheads and some of which would slide into a rubber grommet. Since I already had this other stuff, I went ahead and used what I got from Ss Brewtech.