I've never seen a storage business that utilized shipping containers but think it would work out. Just put a couple rows of them on a piece of property and there ya go. These are fairly inexpensive for used ones ($1500 to $3000) So they would eventually get paid off. You would probably want to paint them all the same color for cosmetic purposes. And you could just keep adding containers as needed.
I have 70 shipping containers in a variety of door configurations that I use in addition to my standard self storage building. I prefer them as they are water tight and don't require building permits. I buy the 1 trip new units and use the metal walls from insta container to make the sizes I want for the 20ft double doors on both ends for 2-10ft units or 8ft and 12ft. I also have some 40ft with 6 side doors and 4 side doors for the perimeter of my property to block snow and wind. Just depends on your location if appropriate with zoning