On one of my drums I use the Weber lid and on the other I have four 3/4 inch holes drilled fairly evenly near the outside of the flat lid. Both of them have the Spicewine temp gauge mounted just under the bottom cooking grate. Before I mounted the gauges I calibrated them.
When I first mounted the I was a little untrusting so I kept using the Nu Temp probes through the holes in the lids. There was a small difference but not much (I don't remember exactly how much). I have gotten to where I trust the SW gauge and no longer use the probes except for the meat.
BTW... I use the Minion method in an 18 inch diameter fire ring. It seems to burn so slowly that I cannot image there being a 50 or so degree difference between the middle of the cooking grate and the outside of the cooking grate.
[SIZE="2"][FONT="Comic Sans MS"]Food! It's the second most important thing to a young man, and the most important to an old one.[/FONT][/SIZE]
Smokin Gators BBQ Team
Medium Amazin' Blue Spicewine - It's a Swamp Thing
Large BGE - Adopted
Medium BGE - Adopted
Weber 22 inch w/mods
Weber Genesis Silver C Gasser
Constant wood lurker