I purchased a shower base and wall set from Lowes. The installation calls for gluing the walls directly to the studs. Two of the walls are outside walls and have paper backed fiberglass insulation in them. If I put plastic up on the studs I will not be able to glue the shower walls to the studs. I am not sure if I even need or should install some sort of vapor barrier in this application since the plastic shower walls will not transmit moisture.