I would like to go further with this and create a notch in the studs so I can push the shower base 1/2" closer to the wall (I need this and I also think that using furring strips as the manufacturer recommends is not the best solution -puts some pressure on the cement board AND ruins the vertical of the wall as the bottom side of the sheet is pushed toward the shower instead of sitting parallel with the wall at the base)
Here is what would like to do. IN this case I might add some BlueSkin between the wood and the shower base
Update: I am not familiar with the best type of drywall or sheet that I can put there and I want to know if there is one that is absolutely guaranteed that won't absorb water.
From the comments and the answers I have received so far I take it that there is no such a thing and going with the lesser evil is the only option
Update2: this is related to this Question