In this I make a burn out kiln for lost wax casting out of a keg. I won't use this for investment casting but ceramic shell or suspenda slurry. its pretty simple and seems to work well.

I used 1" ceramic Insulation.
you will need a 2' wide X 7' long. 5' to wrap around the keg and another piece ~2' to go on the lid.
To seal it I use Ludox and z-wash.