Here’s a thread about making a heat cave: Heat Cave on the bench
You could put the charcoal block on top of any kind of soldering board instead of pumice. If you’re concerned about the charcoal breaking, you could wrap it with wire or use some casting investment to hold the bottom of the charcoal block together in a shallow metal tin.
When a soldering board or charcoal block breaks, keep using the broken pieces on top of other boards and surfaces to manipulate the heat. For example, if you are not using a turntable, you can put the small broken piece on the side of your work opposite from the torch side, to reflect the heat back onto your work. You can use the broken piece vertically, by standing it up on it’s side or leaning it against something that’s fireproof.
Use caution when playing with fire and hot accessories. To be prepared for any accidents, I keep within close range a water sprayer, fireproof mitts, a fire extinguisher and something like this: https://www.aliexpress.com/item/32913704250.html