Wiski...nice job on the mod, it looks great!
Kathy's I fill the firebowl up to about an inch past the holes for the 15 to 20hr burn. The first long burn I used Lazarri lump and the pieces are quite large. This allowed the burn to go 15hrs without me touching it. The second 20hr burn I used Royal Oak which has smaller pieces and I had to wiggle the holes once during the burn to clear them of ash. But even after the 20hrs I still had some lump left.
I have found it key to put large chunks together on the grate then fill the area around them with medium chunks followed by the small stuff to finish off your pile. I'm not sure how well it would've worked out to just dump the charcoal in and fire it up. I also start the burn with only about a fist size ball of lit charcoal placed right in the center of the pile.