Dunno about the "veteran" classification because I still have a lot to learn. (...tinker with.)
My best answer as to temperature probe placement is, place it where it's representative, and make sure that flow is well-mixed.
First, make sure the smoker cabinet's smoke flow is well mixed, meaning that it works
with natural convection to make sure that smoke is evenly distributed. (Fancy way of saying, "Hot air rises, and be sure to throttle it to your advantage.") This amounts to controlling smoke flow by mounting the smoke exit high and constricting it slightly to control smoke and humidity. Don't have lots of vents along the flow path, because at every place that air is introduced or smoke/humidity is released, the composition past (above) that point will be different.
Then, assuming the smoke is well mixed by the time it moves up, away from the air/smoke entrance, past the meat, and gets to the exit, the smoke temperature and contents should be representative of the upper part of the cabinet. Locating the temperature sensor just before the gas stream exit is probably the best location. However, there's something to be said for monitoring the gas stream entering the meat zone, too. You don't want it to be too hot.
I tend to go nuts and place a temperature probe in one of the sausages (for Internal Meat Temperature, "IMT") as well as one in the exit smoke stream, just ahead of the outlet. Then, I place one in the smoke, down just below the meat. ...yup, overkill, I know. But my results improved greatly when I started monitoring both smoke temperature
and IMT. (I also log ambient air temperature, measured separately.)
My smoker is a gas one, but I smoke sausages with an external smoke source and an electric element so I can keep a nice, low, controllable temperature. The bottom is fairly open because of the gas burner, which just sits there for sausage smoking. I control smoke flow with a single top/rear vent.
...and that's one man's opinion. Tinker. Enjoy.
