I am renovating my bathroom in my mobile home because of water that has seeped thru the three "tub walls" and the adjoining bedroom. I have ripped the drywall out, exposing the studs and replaced water damaged studs with new ones. I would like to install that cementitious board for the new walls instead of regular drywall and install a tub-liner manufactured for mobile homes. Will that backer board or hardi-backer tape, float, and look as good as regular drywall when painted? I realize that as a subfloor, it wouldn't matter, but the tubliner will partially cover the middle and lower half of the new wall. Do you float it with regular drywall mud? If not, can the mud used to float it be used in hopper for texturizing the walls before painting them? Also, I plan on laying some ceramic tile down in that same restroom and was wondering if I really need to place some backerboard down as a subfloor? The floor has vinyl on it, and the subfloor is in good shape. Do I really need it?