This is just my opinion, so take it for what it's worth.
I do not see the need to drill into the kettle (lid or bowl) for a thermometer.
The first gen M/T and the first two gens of Performer had the lid thermometer through the lid handle.
As a result, the tip of the thermo was very close to the lid vent.
The tip is what reads the actual temperature.
I put a Tel-Tru thermo through the lid vent on an angle and have had no issues.
The reading is usually in the 35-50℉ range higher than the grate temperature.
Got this idea from
@MrHoss .