A recent online auction netted me a box of K20 soft fire bricks for CA$25. The photo showed maybe 5 or so bricks but in reality the box had 20 bricks, 2 of which already had heating elements!
This is my test layout, the temperature gauge I have peaked out at 1050F but it got much hotter than that. Enough to get a piece of steel yellow in colour. I will now source a PID controller, K Type thermocouple and a SSR to control things.
The elements measure 17ohm and 23 ohm, which when wired in parallel will generate 1440w, or 9.9A at 120V. My test indicated that the wires became sort-of lukewarm at most. The outside of the bricks got warm after letting the furnace sit while cooling off. Looks like I won’t need to add extra insulation to keep the container cool.