It's not specifically about soup can forges but there has been posts recently that covered the plaster/ sand home brews and using castable or ceramic blankets. Searching can be tricky if you get specific, just gotta start skimmin posts in the right category. Good luck with your gas unit though I have been procrastinating with building my freon tank forge with other projects.
IDE be interested In seeing this, getting around to building a burner soon ( hopefully soon lol)