Plumbing and bathroom systems comprised of bathtubs, bathtub enclosures, showers, shower enclosures, fitted bathtub liners and parts thereof, shower bases and floors and part thereof, and various shaped bathroom enclosure wall panels and assemblies, made of steel with a fired-on porcelain enamel coating for use in new construction and for refurbishing, renovating, and modernizing existing bathtubs, bathtub enclosures, shower enclosures and shower bases and floors, bathroom walls, waterproofin...