If I trim things right and play a little tetris I can get 6 STL cut slabs on my 2 rack UDS. 3 on each grate laying completely flat. You should be able to do the same on a 22.5" Weber Smokey Mountain. Check into getting one of those.
Or look at the pit barrel cooker. You can cook 8 slabs (or more if you buy extra stainless hooks) with relative ease.
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS