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The first set of coals is enough to go right to the end of the bake. Just jiggle the ash off of them every once in a while and by the time the bread is done they are still hot enought to maintain 350f in your pot. If your out in the wind you will probably have to replenish them. I use that neat little red bbq I got at wal-mart for $30.00 as a wind break so never have to worry bout the wind.
When camping up at the lake I dig a circle twice the width of my DO and about 6-8" deep then level the bottom of the hole. I pile the dirt from the hole on the windy side of the hole as a further windbreak & place the coals in the bottom.
It works really well. If is so windy that you need a deeper hole, it is too windy to have a fire in the forest anyway so I bite the bullet and make bread in the motorhome.