I used the coal grate from a 22 1/2 weber, a 12 inch tall piece of expanded sheet metal, then welded the grate 2 1/2 inches from the bottom for airflow and it works like a charm.
I use a 3/4" ball valve and have 3 more 3/4 nipples that have been closed since the burn out.Actually I used bulkheads instead of pipe nipples.My fire box is an angle iron fram and stainless expanded metal with a door to slide it in and out for easy refills but I havent done a long enuff cook to need it yet.