hi paul,
ive made a forge out of a cylinder very much like this and it works very well with charcoal. what i did was cut it in the middle length ways and then put the two back together with a hinge on one side, much like a barbecue. Then i drilled a hole in the bottom half big enough to accept a 2 inch pipe which i had drilled holes in, the pipe went right the way to the end of the keg and stuck out the front about 12 inches. I built up fire cement underneath the pipe and up around the sides to hold the heat in and stop it buirning though the sides, i went for a sort of rounded "v" shape on the inside. then leave it overnight to dry and light a small fire inside it to help it dry out.
it worked really well! i gave it to my friend as a birtthday present, i'll see if he can get some photos for you.
nathan