Depending on the campaign setting, a wooden bathtub might make more sense than a metal one:
Source: Wood Hot Tubs, Cedar Wooden Hot Tubs, Wood Heated Hot Tubs, Japanese Bath Tubs and Ofuros - SeaOtter Woodworks. (The one pictured is an elipse cold-dip tub: 4'l x 3'w x 3 1/2'h fits two adults...