I am finishing my basement -- in my bathroom, I'll be installing an acrylic shower pan with tiled walls in the shower stall. Once I get the pan set in the mortar bed and nailed (through the nailing flange) to the wall studs and everyting sets solidly - do I run my cement board down "over" the nailing flange on the shower pan? Or do I run it up to 1/8" of it and use silicone sealant in the gap? I've heard conflicting reports on this. Also - do I use some sort of moisture barrier between the studs and cement board (4 mil plastic sheeting, etc.)?

Thanks a lot.