J Hasselberger
TVWBB All-Star
For your situation, the 18.5" is plenty. I can coil 6 to 8 racks of St. Louis ribs in one cook if need be. I've done a 15lb. brisket (even though I had to "shoehorn" it in between the top grate handles). Once the brisket shrinks a little, it fits fine. I have cooked for 25 people on the 18.5, admittedly in shifts for some of it. If you really need something bigger than the 18.5, get a 24" x 48" offset.
Jeff
Jeff