I read that I need to caulk between my backer board and plastic shower pan where I left my 1/8 or so gap. Is a kitchen and bath caulk what I should use here? Do I caulk now or after I tile or both? I would think both between the CBU and pan and then again between the tile and pan. Thanks for any help with this, just trying to do everything right and the more I read/learn the more questions I have!