Thanks for sharing this.
It sounds a good fix. The company that supplied the back panel have also now advised me that I could try polystyrene to pack behind the panel too.
I am installing a wooden surround and a marfil back panel and hearth.
Because of the depth of the electric fire I will need to use the full rebate allowed with the fire surround.
Can someone advise on how to install the back panel, as it will not be flush against the wall - but will need...