They are also called Wonder Ovens and Wonderbox and I've made a dozen of them (found the instructions on-line and hubby made a paper template and a cardboard template for the pattern pieces). I've given them to family and friends (included a nice stainless steel Dutch Oven with each of them), and I find them very useful.

I kept 4 kinds of soup/stew/chili hot for hours for a New Year's Day Soup and Bread Dinner. In the summer you can also keep cold foods cold when you need to transport them or take them to picnics.

I've also made steamed yeast breads in my Wonder Oven.

This isn't a new idea, there have been many methods of "fireless" cooking, including the Haybox. You may enjoy reading the 1913 book by Margaret Jones Mitchell (of Gone With the Wind fame) "The Fireless Cook Book". This method goes hand-in-glove with my Solar Cooking. And I also use a Thermal Cooker (aka thermal cooker shuttle - popular in Australia, Asia, and the U.K.) as well as small Thermos Bottles for cooking a large assortment of things.

The link below covers a number of these methods.

-Grainlady

Here is a link that might be useful: Thermal Cooking

It gets good reviews and there are a lot of instructions online for making a bag like this this or a haybox oven.

I like the posts from South Africa. A whole world we don't know about.