The owner of a portable storage unit has a lien on all personal property stored under a rental agreement in a portable storage unit for rent, labor, and other charges, and for expenses reasonably incurred in the sale or other disposition of the property under law. This lien is superior to other security interests except those perfected before the date the lien attaches. The lien attaches upon default by the occupant as stated in the notice of default served on the occupant as provided in this chapter.