Spray the surface with vinegar 2-3 times per week. Fill a spray bottle with white vinegar and use it to spritz the fiberglass surfaces a few times a week. This can minimize odors in addition to cutting down the amount of time you’ll spend scrubbing the fiberglass clean later.
Avoid leaving items suctioned to the surface. If you have items in your tub or shower that adhere to the fiberglass with suction cups, remove them. They leave residue stains that are difficult to remove and clean properly.
Polish and wax fiberglass surface twice per year. Use a clean cotton cloth to first apply an automotive white polishing compound to any dull or scratched areas, and then buff with a white automotive cream wax. Repeat this routine twice a year to keep your fiberglass tub or shower looking shiny and new.
Keep your fiberglass surfaces dry. After each use, squeegee your shower or wipe it dry with a bath towel. Doing this regularly will get rid of the particles that allow soap scum to form, which will give you fewer stains to scrub off in the long run. Open the window or turn on a fan when your bathroom surfaces are drying to avoid mildew growth.
Soften your water. Install a water softener to filter minerals out of your water, which contribute heavily to soap scum buildup and rust. Additionally, put epsom salts in your bath water each time you take a bath to help soften it.