Seeing that oven got me to thinking about the Primitive Technology guy who built the hut with only the tools he could fashion in the woods. He used a lot of clay to make the walls and such. One of the more interesting things he did was make a kiln and then fire the clay shingles for the hut. So, with that in mind, maybe the oven could be surrounded by clay and used as a more conventional oven. Clean inside with a burn chamber underneath. Obviously it would be a more permanent installation, but for a long term camp it would give a nice baking oven.