I have a small 10’x6’ bathroom and am completely gutting and redoing it. I have a question about the exterior and kitchen wall (the red lines in the picture). Do I put sheetrock on the tub wall, backer board, plastic anything? The exterior wall should I just put insulation or plastic as well. My bathroom will not have a vent but does have a window. I live in Maine and my exterior walls are set up from outside to inside – vinyl siding, plastic, foam board, diagonal boards to studs, roxal batt insulation, (no plastic) then sheetrock. Any help would be great. Thank you.