Here is where I got the idea, and it only cost me $2.42:
I put the solar cooker out in the sun today around 1pm between work and going to the anniversary celebration. It was mostly sunny and in the 80s. I had to hurry up and think of something to experimentally cook, and I also had to find a dark pot of some kind in a hurry before I left to go to the celebration. I found this small teflon-type red pot. It was small enough that I could place the pot into a large plastic bag as the instructions showed. As for the food item, I found some frozen green beans in the freezer so I threw them into the pot, put the pot in the plastic bag and set it out on the solar cooker. After that, I left for the party closer to 2pm.
Arrived home. Checked on cooker and it was IN THE SHADE! But it did look like it had been heating up while I was gone. There were moisture beads on the walls of the plastic bag and the pot was warm but not hot. I went ahead and moved the whole solar cooker back into the sun and facing west to follow the remaining path of the sun....then I went inside and took a nap--big mistake but I rather enjoyed it!
Woke up and went out and checked on cooker. It was no longer in the sun again and was cool. But it did look like it cooked--the beans were still warm. Actually, the beans looked whitened or blanched from the sun.
--You need to be around to move the cooker as the sun moves. Leaving it and taking a nap was my mistake.
--The sides were a little "flappy" and curved inward at times. You have to keep adjusting it but it does heat up and work.
--Wind could be a major problem and you could lose your food if it tips over.
Overall, my impression is that this is not a real stable setup, and I think I'd rather try building a small wooden box-type of solar oven for more stability. I may have to move on next weekend and try that. It's supposed to rain here all through the week into next weekend so I probably won't have the opportunity to experiment much. This model I've tried is a very good alternative, though, if you have no other options. I believe it *will* work. Maybe I need to go and buy a $6 windshield reflector....