The ones Pedro makes are idiosyncratic; he’s a very experienced metalworker. The only tools he uses are two can openers (a church key and a gear-type lid remover) and a pocketknife that uses replaceable utility knife blades. He’ll make me one in under ten minutes and I’ll throw it away on the last day of camping; I haven’t any pictures I’m afraid. 
All that being said, they are very similar to this, and work the same way:
More elaborate convection gasifiers are also easily built…
And they can be made more durable, too…
EDIT: If you take one of these camping, test it in your yard first - making sure it doesn’t easily tip over or blow out, and that the potholder works with your camping pot. And be careful how you pack it! If it’s put in the backpack with nothing inside it, it’ll get crushed, and then it just won’t work as well, even after you bang it back out.
