Thinking that a caldera cone is sort of an inverted chimney kettle, I was reminded of this at "http://www.bushcraftuk.com/forum/showthread.php?t=54683&page=1" forum, where
"I've been experimenting with an old stainless thermos to create a "reverse kelly" where the flames run up the outside of the inner bottle inside the outer jacket. I've just got to make up a hobbo stove the right size for it to sit on."...
This made me thing a MYOG inside out chimney kettle based on beer can would be easier to build:
Keeps the simplicity of a chimney kettle, other than may have to remove "pot" to add more fuel.
A steel can forms lower part of windshield/fire box, stiff foil/tube the upper, from which the beer can pot hangs: perhaps on horiz struts.
Diagrams are better than words so: