Hi guys and thanks for the response.
As far as gas bottles go for a firebox, I'm after something a bit more substantial. I've been on the mentioned website before and found it very useful. Basically I need about a 500mm cube as my firebox. About the same size as a decent stove!! Bolting it to the cooking chamber is a good idea as I've got a mate who said don't even bother trying to weld it, especially if it's old.
I'll keep my eye out, it could double up as a hotplate for my frying pan!! Endless cooking possibilities...