IMO 3/16 will work fine. I stopped my plates about a foot from the end just cause it looked OK. Maybe TuscaloosaQ if following the thread and can weigh in, certainly more of an expert builder than me.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.