Z,
I'm sure you could. With an old Igloo cooler to use overnight you could heat the interior with stones that were heated in the hot sun. The environment doesn't have to be that hot. Just remember the longer it sits in a heated environment the more "sharp" the yogurt will be. Some people really like that "sour" quality.
I've experimented with making yogurt using just powdered milk, powdered milk and canned evaporated milk,
and whole milk with powdered milk added to it. Each gives a different quality of yogurt. The evaporated milk (not the filled evaporated milk...made with soy) will have a more custard like quality.
As for the fruit on the bottom....I've used pie fillings of apple, cherry, strawberry, blueberry, vanilla,
coffee (instant coffee as a flavor) I've used it straight out of the can and cut down some with thin simple sugar syrup. (one cup sugar to one cup water heated until dissolved and then cooled) This way the fruit stays thin enough you can stir it into the yogurt without having to force it lose (once chilled) and spill the yogurt out of the cup.
little things you learn while experimenting.
I've had friends & family try my yogurt and they have all claimed it's just as good as anything they would
expected to get from the store by a national brand name.
As for Greek Yogurt.....All that has been done there is the yogurt drained in several layers of cheese cloth.
The whey can then be used in other things such as candy, pastry, or other confections. The yogurt will be thick like cream cheese which makes it nice for dips or sandwich spreads when mixed with other foods such as potted meat, ground Spam (or other canned luncheon meats), mayo/ranch dressing, pickle relish, chopped green olives etc, and seasoned with some "season all" or "Soul" seasoning. I like it best on Rye bread with lettuce. But you can tweak this to your taste.
Yogurt can be a building block staple to use in a lot of other foods.