Since everyone was so kind to make suggestions, I wanted to post my results. I decided to use the snake method recommended by Mike Cosgrave, because I didn't want to have to remove brisket to add fuel. I used a lot of large hickory chunks mixed in with briquets. I snaked about 90% of the diameter of the grill, and never had to refresh. I didn't use all the coals. I have a probe that transmits wirelessly, so I put the probe in the meat. Simple rub of kosher salt and pepper is all I used. I rubbed it and let it sit at room temp about an hour. Probe said it was 60 degrees when I put it on the grill. For the most part I was able to control the temp between 250 and 300, trying to stick to the 275 mark. I only had the thermometer in the top of the lid that came with the performer to go by. NOt sure how accurate it is. I guess I can boil water and test it. I had a pan of water sitting over the coals the entire time, and it didn't run out of water. I had to turn the grill every hour or so to keep the brisket opposite the coals. The snake method worked pretty good.
It took another 7 hours or so to hit 200 degrees. by then, I was hungry, and decided to test it. Soft as butter. Nice, sweet, smoky flavor. THere was no possible way that any member of my family was going to let that thing rest for 30 seconds, let alone 30 minutes. How do you guys hold off, after smelling it cooking all day? You've got more will power than I do. It came out the perfect texture. The slices held together for serving, but fork tender to eat. No knife required. I put fat side down while cooking, and the flat stayed moist, it never dried out, and the point was deliscious.
Only downside is that it didn't have a smoke ring. It was uniformly brown, not that edge of red that marks a championship brisket. Don't know why.
Low & Slow takes a long time. I think I'll try a little higher heat next time.
Observations:
The kettle style cooker is not the right tool for the job. There's no doubt it can turn out a delicious brisket, based on my first experience as an amateur. However, if I were going to cook large briskets, or cook brisket more than 2 or 3 times per year, I'd have to get a smoker. There's just too much need to open the thing to turn the grill to stay ahead of the snake. The other problem is that the snake of coals/lumps doesn't always stay in place. In some places it slid down the side, and I dropped my temp a couple of times and had to wait for it to burn around to a better part of the snake. Also, there isn't a whole lot of separation, although it seems to have been enough.
Thanks everyone for the help.