It looks like you're new here. If you want to get involved, click one of these buttons!
I would say there are 3 ways to fit St. Louis ribs on a large without huge investment:
1. use a rib rack (got mine at wally world for $4ish)
2. cut one rack in half so that you have 2 halfs on outside and 2 wholes on inside
3. buy another 18" cooking grid and some plain clay bricks wrapped in aluminum foil. I will go original grid, 2-3 "fire" bricks, then sent 2nd grid on top. That is a $15 way to get 2-level cooking
I use a rib rack everytime I do more than two racks on the LBGE. They cook just like laying them flat. I usually turn them over about mid cook.