Usually, these storage containers have only one point of entry, which can be opened and closed with a key in your possession. The off-site storage facilities usually feature sophisticated security, and some companies offer climate-controlled storage options for precious or temperature-sensitive belongings.
The trucks that are used to transport these portable storage containers usually have special systems in place to ensure the security of the containers, and your belongings, and usually a protection plan is offered in the off chance something happens in transit.