I have the bottom mount as well, wish I didn't. Even with my drip pan there is always grease and drippings accumulating on the bottom. I also don't remove mine,
if your looking for a PID controller the one DirtSailor links to is good, but the duel probe controller is by far the best and worth every penny.
http://www.auberins.com/index.php?main_page=product_info&cPath=8&products_id=381
ive done 2 builds with it, and working on a third.
You can also use a finned strip heater, as high a wattage as you want so long as it fits dimensionally. The key though is you have to use the dual probe I linked with a finned strip heater. The reason being is that it can actually be programmed for the total power output. If you run a finned strip heater at full power with no forced air then they burn out. You can drop the total power output with the dual 1800w controller to match the max watt per sq" for still air ovens. They work very well with this set up. They also have a smaller footprint in the bottom of a fridge smoker, I use a sink drain under the finned strip heater for air intake and it doubles as a clean out drain.