Improve ventilation by using an exhaust fan, squeegee water off surfaces after use, and apply a mold-resistant silicone sealant.

Mix equal parts white vinegar and water, spray on the doors, and wipe with a microfiber cloth. For tough stains, use a baking soda paste.

This requires significant remodeling but involves sloping the floor properly (1/4" per foot) toward the drain and using waterproof membranes. Consult a professional for plumbing adjustments.