I have used each of the products mostly described, the Outback Oven, the Bakepacker, and I've made reflector ovens similar to Old Scout.  The ovens I've made come in two sizes, one the same size as OS to fit a round baking pan and the other to fit a typical frozen sized pizza or a regular size cake pan, about 13" square.  Another thing mine have is a back door that opens so you don't have to pull the oven away from the fire to rotate the food and the other is that all of the pieces stay attached to each other, except for two wing nuts, and yet it still folds up flat.