I have never replaced a tub with pre fabricated tub surrond walls. But, i would think the installation would be much the same as with any other standard tub surround materials used tile etc. As a good practice i checked with some contractors/tile setters/masons and the vapor barrier they suggested that i use for the surround was roofing felt paper i affixed to the studs. However, some said the vapor barrier is only needed at the one block exterior wall where this bathroom i remodeled was located. Then the tub is set in place attaching the tub at stud locations (most tubs come with attaching clips) and plumb up the tub drain. Run your green board,and where it meets the tub flange it might bow in after attaching the board...keep a level handy to check how level the board is and for high and low spots that if unacceptable can make for a wavy tub surround wall.In which case you might have to fur out the studs as necessary to make for a flat level wall to fasten your board to ,and adhere your pre fab walls to.