I tried a couple different way to slide in a 12" thermometer and the easiest, cleanist and least expensive ($1.00) was a stainless bolt, drill a hole through it (used the drill press at work).
Drumhead - UDS x 2 & UDG
Keep on Smokin'
KC native missin' KC
IMBAS Certified MOINK Baller 2009
I also support PETA - People Eating Tasty Animals