what cone do you want to reach? you could do nothing & do saw dust,
pit fire style fires. go too high & the can melts.

Kaowool cloth insulation can be used, but it's not too cheap. get the
thinest koalwool, maybe 1 inch thick, and you can do some bisque fires.


if you smear the walls of th ecan with fluffy clay, a few inches thick,
you reduce your chamber volume but might get buy with something.

fluffy clay could be high temperature clay plus vermiculite or inert
materials that burn out like saw dust.

i priced vermiculite a few years back & it wasn't cheap.

see ya

steve