I started to make the collapsible solar box cooker a couple weeks ago, then left it half done while conflicting design ideas swirled in my head. I began this project knowing that I do not like reflectors. They are just too big of a nuisance on a windy Hemet day. But on the other hand, it sure is nice to ramp up the oven beyond the 200-250 degrees F that a reflectorless solar oven can reach.
I have received much interest in presenting my solar cooking. I feel obligated to make an easy traveling oven so a modified collapsible oven is the best solution. I will post pictures as soon as I finish it. In the meantime, here are original directions. I am doing all of it but the lid. I plan to simply rest a glass window top for the lid. My oven is ginormous at 23″ wide by 39″ long. I plan on setting it on the hood of my car at the park so folks can stop by and learn about solar cooking while my very energetic son plays with his friends.
If you want help making your own solar box oven, start hunting for glass. My favorite is framed tempered glass windows from RVs and storm doors. Once you have the glass you can make a custom box for it following the directions below. If you want me to talk you through it, then contact me once you have gathered your supplies and read the instructions. We can meet at the park. I will be glad to help raise up more solar cooks in our valley.
The following instructions are from Solar Cookers.org:
How to Make a Collapsible Solar Box Cooker
It is pretty simple to make a collapsible solar box cooker from two cardboard boxes. The trick is to cut off the bottom of each box, creating two pieces: the base; and the sides. After that, it is possible to collapse the box by folding up its sides and laying them into the base; or, when you want to use the cooker, insert the sides right into the base (Figure 1), extend the accordion sides, and fold the flaps down inside (Figure 2).
The instructions below only show how to make the collapsing box part of the cooker. The top can be built following the instructions for the lid on the Minimum Solar Box Cooker.
You can find the complete instructions at http://solarcooking.wikia.com/wiki/Collapsible_Solar_Box_Cooker.