I have a prefab shower and tub in my bathroom. I am going to pull the it out and install a new tub and tile up the walls. I want to do it right by removing the drywall under the prefab, install cement board before installing the tile.

My problem is that the building was made with metal studs and on one wall one there is double dry wall (on the long wall). My unit is adjacent to another condo unit so the wall between has two layers of drywall.

The questions I have are:
- Do I need to put up a moisture barrier (plastic) on the walls prior to putting up the cement board?
- How do I handle the double layered wall? Remove both drywall layers and install double cement board? Remove on layer and install the cement board?
- With metal studs what is the best way to put up the cement board? Do I install it same as wood studs?

The double dryesll is for fire code, do not remove. Install the cement board by long screws into the studs. Rent a screw gun.

You mean to install the cement board over the two layers of drywall? That does not seem correct. If install a premade base how would I attach that to the studs? And if I were to build a base from thinset wouldn't I need to frame that in from the studs?

Most people will screw thin backer board over the drywall. Whatever you plan to do, I would be EXTREMELY hesitant to remove a firewall. You put yourself in great liability by doing so. The pan can be screwed to the drywall which is probably 2X 1/2 or 5/8 FireX whatever is your local code. Most commercial buildings use 2X5/8, one sheet vertical and 1 horizontal. Think carefully before proceeding.