If you are recirculating the wort, you can get a good measurement from the skin of the vessel. There are a few things you need to make this work:
1. A non-insulated vessel with reasonably good heat transfer coefficient. The converted brew pot should work fine.
2. Sufficient insulation. This is needed to prevent external ambient air temperature from affecting the reading. Note that a 6"x6" piece of closed cell foam will work well.
3. Placement of the probe in a location that has moving fluid on the other side of the vessel from the probe.
While the thermowell is a standard practice, industry is starting to use more surface mount measurements. The advantages are less cost, no leakage, and less contamination. And accuracies are within 0.1 C with proper installation.
This might be something to consider for your setup.