[PeterW]

I've been watching this with interest, and I'm really impressed with the re-use of old stuff...!

One think I did think, is expansion of the steel. This might sound an odd suggestion, but why don't you add a thin layer of a compressible fibre insulation, such as 10mm of rockwool before the outer refractory..? It will allow the steel to expand but not crack the casing..?

Just my 2p

Cheers

Peter