Yes, the recipe I was using called for coals in the hole, then set the DO in the hole, then coals on the lid, covered with a thin layer of dirt. Everytime I took the DO out of the hole the coals were only 3/4 burned, the DO was warm, but the beans were always hard still. I will say it retained heat 12 hours later... but never cooked enough, obviously due to the charcoal going out. I played around with the hole size and depth some, but could never get the charcoal to stay lit and still bury the DO like I was supposed to.
ETA: without soaked navy beans that were still basically hard, it may have worked. Or if I precooked them first. That would not have stopped the coals from going out though.
Give us this day our daily bacon.