ethanol burner and firebox

Hello Everyone, First-time home owner/poster here! I have purchased an ethanol burner to be recessed into a wall in my living room EB3600 - Ethanol Fireplace Burner Insert (http://www.ignisproducts.com/eb3600-ethanol-fireplace-burner-insert.html). The manufacture sells a firebox for the burner, but at $4,500 it is too rich for my blood Ignis Ethanol Fireplace Insert FB3600 Single Sided (http://www.ignisproducts.com/fireplace-insert-fb3600-s.html). I am building my own custom firebox, with the manufactures specs, but have a question regarding the heat given off by the ethanol burner itself. Unlike a traditional gas or wood burning fireplace, the ethanol burner does not produce a lot of heat. It is more for looks than anything else. It is however fire and as a former firefighter myself, I’d like to make sure I don’t burn my new house down. My question - If I build a metal firebox, could I wrap it in Durock to act as a barrier to heat given off by the burner? I’m hoping the Durock would prevent any radiant heat from transferring from the firebox to exposed studs/insulation behind the drywall. Thank you very much for you recommendations.