Very Cool.  I am always amazed with the containers folks come up with to make biochar with.  I can certainly see some benefits to a longer container for longer material and the lightweight and low cost and availibility of sheet metal is certainly appealing for many applications.

Another readily available steel container with a tapered side is a common dumpster.  I'm sure someone else has thought of this but using steel dumpsters and a trash truck for portable biochar production/collection would be pretty slick IMO.

Rowdy Yeatts