What are the gas/fuel specs on this forge?? I see the air/gas mixer and burner - how big a propane tank and hose connection is recommended?? And what is the rate of gas consumption?? (Guessing a 20# HD home tank isnt gonna cut it!!)
If you want to retain heat while having the solid bace, you could make it one brick deeper and set the soft well insulating on the bottom with the more solid harder more stronger brick on top of it. Giving you the best of both worlds.