Here is what my modified ecb looks like. I cut about 12 3/4 in holes in the bottom of the charcoal pan and put a weber charcoal grate in the bottom. The ash drops through to a disposable pie plate. I wrapped the exterior in aluminum flashing and cut three 3/4 in holes in the flashing to allow for air control. I also cut 4 1/2 inch holes in the lid and wrapped the top with stove gasket. I'm pretty happy with it and can get a solid 7 hours at 250 degrees on single pan of kbb using the minion method.
WSM 22.5, Modified ECB, ThermoWorks TW8060