I’ve looked at a couple of 8’ X 8’ exterior double doors on a Napa Valley winery that were built from mahogany panels on a welded steel frame.  My initial look at the doors was to consult only as a custom builder/specialist.  My first impression was that the doors were reacting to extreme weather changes from very hot and dry in the summer to cold and wet in the winter and that the steel superstructure was not moving in tandem with the affixed panels as the panels were splitting apart.  The doors had not been in place for a full year and subsequent visits to site measure showed even more extreme cracking and splitting as the wood dried out through the summer months.  I’ve drafted up shop drawing, proposing a tenoned laminated veneer lumber stile and rail base with rigid foam panels and a 1/4” CDX “skin” as a base for 3/4” rift sawn white oak horizontal panels with 1/4” reveals with a simple 3/8” lap joint to allow some movement.  My lead man and minor partner in the business feels that doing the job is going to tie us to the job for life, repeatedly repairing and rebuilding the doors because the extremes of temperature, moisture and direct sunlight will cause the same issues down the road.  I estimated the job with a pretty big bonus but … not enough to do the job twice.   My instinct is that the engineered wood core will move in concert with the oak overlay and the entire construction will hold together much more reliably than the metal/wood differential movement.  Thoughts?