White Suv in Mining area

Respected Members,

I have two SUV's one being a white one purchased just a month ago. I have found that it has begun to look dull since about 2 weeks. The Cars are kept in the open and usually run inside the plant and the mines and are washed regularly with Turtle Carnuaba wash or KOCH-Chemie. Should I invest in a ppf or a good ceramic coat. If yes which one should I do ? I just want to preserve the bright white colour.