I'd like to improve insulation properties of my bathroom so, as I plan to retile, I thought I could use some brand of tile 'backerboard'. However, I have only about 30mm to play with - can I fix the board straight onto the wall, or must they be mounted on battens? Second point - do I need a moisture barrier behind the board? thirdly, do I need to do anything with the wall that's hidden by the bath, to prevent condensation? Any tips welcomed!