The easiest way to make a thermometer mount requires a drill press or milling machine with a vise. Clamp a piece of scrap metal, then drill using a 27/64" bit. Do not remove the piece from the vise. Clamp a 1/2-13 tap in the chuck and lower the quill with one hand while starting the tap with the other, until the tap gets started, then loosen the chuck and raise the quill and put on your tap wrench and finish tapping the hole. Now
you have a 1/2-13 tapped hole in line with your spindle axis. Screw a 1/2-13 short bolt into it, and through drill it with the size of your thermometer stem. You can make several at once for multiple smokers if you like, or change the bit for different things.
On your smoker, use the skinny step drill in your set, the one that only goes up to 1/2", and run it all the way in. Use a jam nut on the inside with a wrench to tighten your thermometer holder. Now you can just slip your thermo in easily, and take it out which can really help with clearance for removing the charcoal basket.
It's a lot easier to do than to write, and there are much easier ways to do it especially if you have a metal lathe, but that require more sophisticated machine tools.