I bought a dryer exhaust vent, jammed it into the top of the BGE, and put the other end into a cardboard box. I made some effort to keep the box higher than the fire but that's about as much thought as I put into it.
The fire was 300F (per dome thermometer) and I had to refresh the apple wood chunks a few times.
Temperature in the box was 67F, about 5F higher than ambient. There were a couple of pounds of cheese on a grate in the box. I cut a sample and it's definitely strongly smoke flavored, but it isn't ruined with creosote, either. After a couple of weeks of resting, it should be pretty good--based on what I have read.
This thread gave me a lot of info: