I use rolling some of the time, or rib racks the rest of the time, depending on what is in the cooker at the time. You can get 6 to 8 racks on a single grate if you roll and skewer.
They will end up banded, (color light and dark), where they touch themselves on the roll, if you leave them rolled till they are about 45 minutes to an hour from cooked, you can unroll them and finish them on a kettle, or lay them out flat on the grate and let them flatten out and gain some more color from, a spray or 3 of apple juice.
You are only doing 6 racks total, so you could do 3 on the top rack and 3 on the bottom rack if you use a rib racks, if you do use rib racks, lay the meat on the top rack directly over the meat on the bottom rack and let the juice from the top baste the ones on the bottom, switch the bottom to the top after 3 hours and then let the ones that were on the bottom, baste the ribs from the top that you moved to the bottom.