I am going to build a hearth ( I know there are a lot of threads on this). I have been researching the r-value thing and i see that fiberglass insulation batts have a 3.33 r- rating. So could i sandwich that between 2 sheets of wonderboard to get the needed r-rating underneath my stove? If so would that work on the wall to reduce the distance the stove has to be from the wall?? I only need R=1.2 underneath my stove. Thanks!