You can construct solar ovens that produce heat in excess of 350' F., with inexpensive materials. There are a great many plans available on line. Usually, if you are in a sunny location, a simple sheet metal box, with shelves for the food, with the outside painted flat black, or better yet, solar black, is all that's needed to cook outdoors, or at the campsite with a solar oven. Excess heat is controlled my opening and shutting vents.
Of course, there are well regulated, more efficient designs available, again online, but are more expensive to build, and may require a little technical expertise.
To answer your question, low temperature cooking may be fine for heating up a can of soup, or beans, or even pre-made pasta. But you aren't going to want to make things from raw ingredients, as you'll need to get the heat high enough to kill the little, live nasties that crawl around in food, and on surfaces. You will need to bring the temperature of the food up to 145' before you start killing bacterial and such. Higher temperatures are needed for some micro-organisms. So unless you know you can get the food hot enough, in a relatively short amount of time, don't do it.
Now drying foods, like sausages, fruits, jerky, and veggies relies on other agents inhibiting the growth of the bad things, such as high concentrations of sugar, salt, pink salt, or acids. But even then, you need to do some research to do it safely.
Seeeeeya; Chief Longwind of the North