I do not have a PID yet so I am using a regular meat probe to measure the cabinet temp in the OBS. I put it between the drip pan and the bottom rack. It seemed to be way off from the door thermometer. I had a 8.5 lb butt and a 9.5 lb brisket so there was alot of meat blocking the heat. I would start to get inconstant readings from this probe though. One time it spiked up to 176 degrees. I opened the door and some grease had dripped onto the probe causing it to spike. Another time fell onto the drip pan and that seemed to make the temp spike.
So just throwing the question out there, where do you mount the probe for the cabinet temp to get the best results?
Put the probe just below the lowest rack with meat on it. You can use a couple of paper clips to make a hanger for it.
You want to get a reading of what your meat is being exposed to. Both sources of heat are at the bottom. Bottom rear and bottom left as your looking in. I recommend that you put the probe just below and to the side of the lowest rack that has meat on it. If you have multiple racks of meat, just remember that the ones above are being exposed to less heat.
Jimmyb - Arnie beat me to the punch - I have never hung mine but I feed it through the vent and let it dangle just below the lowest rack. I also have it out front, near the door so that it doesn't get dripped on and it's easier to grab and re-route if I need to move a rack. I was also advised to stay away from a permanently mounted sensor. Hope this helps.