A Wonderbag works very well. BUT.... It's big. It requires a lot of space. It's size is a negative for me because I have a very small camper. A pot with a handle does not work well in the bag. If the cooking container is not leak proof, the contents leak while in transit.
Amazon has a cheap ($40.00) thermal cooker. I've only had this a few days, but preliminary experimentations have me wanting to kick my own butt for not buying it sooner. As a comparison between the Wonderbag and the thermal cooker, I'll use the example of making yogurt. Yogurt is cultured at around 115 degrees. After incubating for eight hours in a Wonderbag, a batch of yogurt will have lost its heat. Amazingly, after fourteen hours in the thermal cooker, the yogurt was still warm. Remember, that's a starting temperature of only 115 degrees. With the Wonderbag, after a long day's drive, the meal that went into the bag at boiling temperature that morning was cooked but needed to be reheated. I'm thinking that with less heat loss in the thermal cooker, the food will be safer. Plus, the cooking pot is contained within the unit so no worries about leaks.
I have not attempted Danny's suggestion with 'straw-boxing' a pressure cooker. I can tell you this--a four quart pressure cooker is so much quicker to reach pressure than a six quart. It drops pressure faster too making it far more time and fuel efficient. Since it takes so little time to cook in the four quart, I've never felt inclined to straw-box it. Hope this helps.
