Sadly, storage units are not invincible either. I think it was in 2006 my Uncle put most all of his tools in two storage units in a Dallas unit. There were some other storage unit "onlookers" as he & my cousin unloaded all of the tools in it. They came on to the lake & fished with us all weekend. On heading back, his phone had been off & received a message from a call made previously. It was the unit manager asking if he wanted him to put locks on his units. He knew it was not good & headed straight on to the units instead of home, after dropping my cousin off. He had put locks on both units after they stuffed them with tools. Some Craftsman tools wwere from the 1960s including 2 upright boxes. Some tools or machinery were brand new, never used. When he arrived, both units had been picked clean. Well over $5000 worth. He was sour about going fishing for at least a year. He told the police about the "onlookers" were the best possible suspects. Obviously they took their time investigating it, as they finally caught the culprits. It was definitely the "onlookers", but a year later, so all his tools were long gone.
In the past year, my sister had 6 storage units filled with merchandise acquired from garage sales & repo-ed storage units. They had a major amount of units hit in a spree. Her units were included. It looks like all she was missing was tables & chairs, but since she had so much, she did not truly know of everything she had.
So, storage units are not always the safest bet either. I know, not cheering you up here, am I?