I want to build a hearth pad for a Regency Hampton GC60. It will go on a hardwood floor in the living room (I'm not ready to commit to ripping up the floor for this). It doesn't mention any heat/insulation/rvalue. What would be the easiest thing that looks decent? My current plan is tile on concrete backer board / durock on felt to protect the flooring. Improvise something for the trim. Would this work? Most people add a layer of plywood. Why is that?