Steve,
How did your cook go? I, too, had 2 butts (~7 lbs each) over a brisket (~12 lbs). This was my first waterless cook using the Piedmont pan setup. This cook surprised me. Fuel and temps were not the problem - completion time was. Previous cooks similar to this had the brisket done in about 13 hours, and the butts in 18 to 20 hours. This time the brisket finished in about 11.5 hours, and the buts in around 15 hours. Could the dry cooking environment had something to do with it? Cooking temp was 240 to 250 measured at the lid.
The bark did seem to be a bit crisper.