I've been reading a bit about bathroom drywall options, and have seen that "greenboard" water-resistant drywall is not recommended for use in the shower/tub wet areas for tile backing. Does that hold true regardless of what material is installed on top? We are having floor-to-ceiling acrylic panels installed for the shower. It seems these would be less water permeable in the long term, since there's no grout to deteriorate and allow water to seep through. But is it acceptable/up to code to install these acrylic panels on top of greenboard? Location is NJ, USA.