Ok, based on many designs here, I built this over the past 2 weeks. This was to replace a MES that had bit the dust (twice)/ The goal is that it will be electrically heated (I hope) using . We'll see later today. Still have to put some racks in there, but should be ready to go. It is nearly air tight, with a small leak around the door (1/16") that I will fix today. The construction uses standard pine 2x4's with 1/2" durock interior and 3" of stonewool all around. The only part that isn't insulated will be an exhaust hole on the front. One question for the Gurus here - Seasoning - do I need to do this on the durrock ? Same as steel ?