Has anyone been charged for stealing their own stuff?
Yes, if it can be shown that someone else had lawful joint-possession at the time. But it's not clear, to me, from the question whether the storage unit manager falls in to this category - assuming she does, the relevant case law is R v Turner (No 2)  1 WLR 901:
The defendant took his car in to a service station for repairs. When he went to pick it up he saw that the car was left outside with the key in. He took the car without paying for the repairs. He was liable for theft of his own car since the car was regarded as belonging to the service station as they were in possession and control of it. Source
Partial answer as there's burglary to consider, which I will return to later when I have more time.