You might take a look at the SnS kettle for guidance. They put it on the same side of the vent which makes better sense, at least to me. But their's seems a bit high.
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Also, Chud's BBQ installed a dial thermometer on his. Again, he had one already on the opposite side of the vent, so he put his mod one on the same side of the vent, and very low.
I installed mine the same way, on the same side of the vent. Mine is about mid-way between the SnS version and the Chud version.
Mine is amazingly accurate. When I put a probe on the grate, the dial reading is very close to the probe reading. So that's nice.
Be advised, my first thermometer, which was a Tel-Tru, blew out on the first cook. I think I was doing chicken wings and the max temp on the Tel-tru was 550. So I got another one but a cheap one on Amazon which maxes at 800 and it's been fine. Besides, IMO, you don't really need a Tel-tru for this kind of deal.
If you want, you can put a second one on the opposite side of the vent but up high like Weber. Best of both worlds.
Think about the length of the stem and the height of the install. You don't want the stem interfering or too close or stabbing at your food while cooking indirect. You also don't want the stem to snag onto the rim of the kettle when you're trying to hang the lid on the side of the kettle.
Good luck