A suggestion:
Our favorite way of doing burgers the past few years is to load a 9 X 13 cookie sheet up with 3 - 4 lbs of ground chuck, top with bacon, cheese, onion, whatever you like, and smoke-roast them until done. NO FLIPPING!!! When done cut them into 8 burgers and serve on Texas toast.
You should be able to fit a 9 X 13 cookie sheet down onto the grate with no problem, and the temps in a Pit Barrel should work perfectly for this.