I live in trailer, and have a garden tub 4'8" deep to corner wall and span of up to 7' feet to allow for electrical switch upon entry. I want to replace this with an extra comfortable shower with low step into shower pan base and new walls. I will bring up the water flow to create the shower spout(s) one for me and one for him. What do I make the walls out of and how do I waterproof the walls. Will I use the plastic sheet for the pan as well as the walls? And, to make it deep enough to use a shower curtain and not doors, how do I do that. Thanks, Laura, Ariton, AL