I am remodeling my bathroom, and the last step is the tub. The Place for the tub was about 3 inches longer than the tub, so we built the wall out by putting drywall over the studs.
I keep reading about cement backer board and a vapor shield. What are my options as i already have drywall behind the tub (stopping at the tub) but behind it. Can I put roofing tarpaper over the drywall and then secure cement backing, or what?
I'm not sure what to do, this bathroom seems to be build a bit oddly.
See pictures below:


