Here is the intake I have been using for the past few builds I have completed. I didn't come up with this design, I found someone on here that used it too. It's some scrap aluminum approx 1/16". I has 4 1" holes which has the surface area of Pi (3.1416). There is no trouble controlling air flow. A buddy of mine cooked 60-70lbs of pork butts on it at one time and had zero problems maintaing heat.
Just thought I would share it with everyone.