You are missing one other issue: it seems easier than it really is. There are only so many people who would use self storage. You see a full self storage place in town and thing you can get a share if you just build one. What you don't understand is demand is not elastic: if you build a second site in town you go from 100 units with 90 used (a good usage rate), do 200 units in town but still only 90 used.