I think I figured this out. So I am doing ribs right now. I am using regular kingsford blue. You do not need to fill the grate all the way to the top. I filled it about 3/4 of the way full. Then put about a half weber chimney of lit coals over that. I am using the 18.5 wsm. The wood doesn’t fit directly under the water pan of course. But I have found that’s not where you want the wood. You want it on the outer edge. So this let’s me fit the wood on with the water pan with no issues. I am doing a brisket cook for Christmas Eve. So that will go for at least 12 hours in the cooker. I am going to test tonight to see how long these coals stay at 225. But I know that my last brisket cook with the weber charcoal I filled the grate all the way up and then a half chimney of lifts coals. They lasted well over 24 hours with all the cents closed. I am thinking 1/2 to 3/4 of unit and half a chimney of lit of the weber charcoal will easily last you the 12-15 hours it takes with wood on outer edge and water pan.