I just found this thread and thought I would chime in here. I received this same Brinkman as a gift almost a year ago to replace my Chargriller that was involved in a horrible accident. Now I haven't allowed so much as a briquett of charoal within 40 feet of it, strictly a stick burner, so my results will be different than yours. The only "mod" I have done is flip the charcoal pan for the cook chamber upside down and butt it as close to the fire box side as I can as a sort of tuning plate. The second I got the last bolt in putting it together I shook my head in disappointment. The fire box door sagged and left a gap, not to mention all the gaps around the cook chamber lid. I have done several cook on it this year with fantastic results. Out of the box it was hard to control temp, either too hot or too cold, lots of baby sitting. I burn nothing but orange wood, and have been using small "logs" about a foot long and about the size of a coke can. After much trial and error I learned when to add wood, when to adjust the box vent to keep everything happy, but still monitored every 10 minutes.
Recently I borrowed a small electric log splitter and made a bunch of splits still a foot long, but about the size of a quarter to 50 cent piece. I have been able to keep a temp of 210 or 400 or anything in between with the small splits. Still got to check on it, but only every 1/2 hour or so. Mid month I did a rack of ribs, small pork shoulder and some chicken quarters, took about 1 and 1/2 wheelbarrow loads of wood for a 7 hour smoke using the bigger stuff. Christmas I did my first Turkey and used less than 1/2 wheelbarrow of the small splits maintaining 260 for 5 hours. Bottom line, I have learned it is a combonation of how much how much wood (with the turkey after building the original coal bed with several sticks I usually only had 1 or 2 sticks going to maintain temp) and knowing when to put it on. One other trick I have always used, both with the Brinkman and my old Chargriller: If I need a little more heat I use a set of tongs to prop the firebox lid open. Gives about a 16th, maybe a 1/4 inch gap at the most, but that little extra airflow helps a lot, especially right after throwing on a new stick that needs to catch flame. Don't wait untill it is on the cool side to add fuel, and don't wait until it is too hot to shut the fire box air vent. Learn to anticipate what it is going to do, and react before it does it.
Out of the box, acceptable results though a little disappointed. After nearly a year of trial and error, great results and happy with it. Until I hit the lottery and can buy a Jambo, or custom build my own.