Mix 1 cup of oxygen bleach and 2 gallons of hot tap water in a bucket. Stir with a wooden spoon to dissolve the bleach powder.
Scrub the plastic enclosure with the oxygen bleach solution to remove mildew and other buildup. Rinse well.
Wipe the enclosure with a microfiber cloth. Allow the surface to dry completely for at least one hour.
Mask the edges of the bathtub enclosure with painter's tape. Make the mask three widths of tape wide to protect it from overspray.
Shake the spray paint can for one full minute.
Apply a light, even coating of spray paint for plastic on the enclosure.
Wait five to 10 minutes, then spray a second light coat on the enclosure. If necessary, apply a third coat of paint.
Remove the painter's tape. Allow the paint to dry for two days before using the tub.