I had an opposite problem with my BBQ. It is built in & too close to a glass mosaic backing. As it is a double skin I inserted insulation material (about 1/2inch thick) into the cavity and it retained the heat. Should give you the same result. The material was made for kilns & can withstand exceedingly high temperatures- I recollect it wasn't cheap.
When you stop horsing around it is time to fire up the BBQ & Smoker