Gentlemens:
FWIW, my high end, de luxe bluing setup use two $20 2-burner propane camp stoves from Wally World. Set up end to end they put the four burners evenly spaced along the boiling pan. It works quite well.
I have a stainless tank, which is probably ideal, but I have heard of folks successfully using a tank made from a lenght of aluminum gutter with end caps sealed with high temperature silicone sealant. Haven't tried it myself but it ought to work and wouldn't cost much to experiment with.
Merry Christmas to all!
Glenn
