I tried to see if anyone posted this before, but i think not. I thought this was a brilliant piece of kit, so simple it is.
http://www.bushcraftliving.com/waxstove
http://www.bushcraftliving.com/waxstove
A good idea is worth repeating
Good clean soot that works well with resin for glue however.
Rub a bit of soap on the bottom of the pot first. The soot washes straight off with the soap.
Eric
You can use sawdust instead of cardboard