Success!
I took a handful of rice, a handful of lentils, some dehydrated veggies, some garlic, some curry powder and put them in a pot. I heated up some water to boiling, filled the thermos and the pot with the hot water. Then I closed up the thermos, and brought the rice/lentils to a boil. After 5 minutes I poured out the water from the thermos and poured in the rice/lentils. I laid the thermos on its side.
5 hours later I sat down to a great meal. I ate it before I thought of getting a picture.
This is a winner.
5 years later: Gave up on thermos. The cleaning out was way too long and messy. Somethi