There are other ways to cook with the sun than in a cardboard box. 

Here’s an open reflector.  This one can be purchased on ebay for about $30. 

http://solarcooking.wikia.com/wiki/Windshield_Shade_Solar_Cooker

This one is made from a reflective windshield covers (the kind designed to keep your car cooler in the summer.)

http://solarcooking.org/plans/newpanel.htm

Here’s a page for making a similar style reflector from cardboard and foil.

This oven is also for sale on ebay for around $50.  It fascinates me because it folds down very compactly–perfect for those with small amounts of storage space.

And here’s a video of a man sun roasting a 6 lb chicken in Ontario Canada on a windy day in February!  He paid so much for his supplies for his slow cooker that he could have purchased this one and come out ahead (since his didn’t turn out as well as he had hoped.)  But I love that it shows you don’ t have to live in Arizona to cook with the sun.