I recently installed a Three Piece Acrylic Mirolin Shower, part of the instructions said to caulk behind the unit were the pieces join, as this is a retro fit into an existing house how would anyone do that and is it 100% necessary, of course I don't want moisture behind the unit and putting caulking on the facing side sort of takes the look and appeal aware from having this type of unit, however, will my bathroom fan (120cfm) be enough to pull that moist air out of the room, thoughts?