Hi, I have ripped out my bathroom and now beginning to put it all back together. I'm back to the studwork and have just ordered the hardiebacker to reboard the walls. I have a mermaid shower panel system for the shower enclosure, they are acrylic coated marine ply with jointing system. Its my understanding I do not need to tank behind this as it should be 100% water tight for 15 years. Do the regs for tanking only apply to tile finishes? Would anybody tank anyway? Thanks