instead of lighting all of the charcoal at once, I light the charcoal at one end of the labyrinth and let the fire work it's way to the other end. Only a few coals are lit at a time and the temperature runs quite a bit cooler. Also, the coals last longer. It can hold temp at 250 to 275 for three to four hours with out messing with the fire.
Another mod I made is to add 1/2 inch of concrete board to the outside of the box that acts as insulation...it holds the heat in for a long time.