I started out with a similar Brinkmann years ago - never could get the thing to reach and maintain temp, but then again I didn't try making any modifications to it either. Even if all you can use it for is parts you made a good score though.
well i tried it today. i almost filled the pan with kingsford briquettes mixed with some lump. i got up to the first line on ideal. i figured it was maybe 200-225. i had drilled a small hole for my meat temp lead so i just stuck a thermometer in the same hole. the dang thing was on 350!!! stayed there for about 4 hours. good thing it did not get to the middle of ideal. think i am gonna install a permanent gauge on it.
here is the spatchcock chicken that i cooked today. i know it looks burned but that is just the rub. (lots of dark brown sugar) actually it was very moist.