Update - last night I got better temps, and at one point it even went
too hot. Time before last, I drilled tons of holes in the pan bottom
and a bit up the sides. I also added some mesh (heavy chicken wire
folded twice - 4 layers) to the bottom of the pan. That didn't improve
the temperatures much. This time I put a piece of a brick between the
chicken wire and the pan to create a 3" airspace, and that seems to
have done the trick. The biggest problem was the ash clogging up the
airflow and insulating the coals, which the raised mesh now allows to
sift down. Now I think it's just a matter of learning good fire
management.

For my next trick, I'm going to try to seal off the lid as suggested,
and make an adjustable vent in the top instead.

Thanks for the tips,
--Jeff