My wife has been using a Wonder Oven or box for quite a few years with great success. She uses them for cooking and transporting foods. When we go on a camping trip or picnic she will bring something to a boil and place it in the oven, when we arrive, we have a hot cooked meal ready for us. Be sure you bring it to a good rolling boil and heat it clear though before placing it in the oven. Because they are well insulated they will do double duty and serve as a cooler, they will keep ice cream frozen for longer than our store bought coolers.
They save energy since you only have to bring the food to a boil and insert in the Wonder oven. For those of you who are not familiar with one they are a heat retention cooker. In other words, they cook the food with its own heat. See WONDER BOX COOKER, A MUST HAVE!! And do a search of this blog for more information on the Wonder Oven/box.
You can bake, cook stews or whole chicken and roasts in them. Because they are a slow cooker and the lid is sealed on tight they give off very little odor, use little energy and would be useful if you had to hide the fact you were cooking from others.
They are very simple in design, my wife makes them, you can see her design at WONDER BOX OVEN/COOKER. Once you understand the principal you can improvise them out of almost any insulating material. At the time of the American Revolution, they called them hay boxes, because they used hay for insulation. You can even make them out of sleeping bags, blankets or towels.
In the following you tube you can see my wife cook a chicken in hers.