Hello Fiona,
Most companies have to take out insurance to meet a number of legal requirements. Sadly it is not a legal requirement for storage companies to hold insurance against the loss or damage to their customers property whilst in their custody - though some might, and in my view all should.
Many insurance companies will not cover your caravan unless it is stored at a 'secure site'. CaSSOA sites are supposed to meet the insurance companies specifications, and by inference that means they should be secure!
But are they? If your caravan is damaged by an intruder who gains access to the site, who has failed? Well obviously the site, because the security measures have failed to prevent the intrusion, So why are you expected to cover the cost of the damage through your insurance?
It is my view that if the advertising or the name of a site includes the word secure or any other words or phrases to encourage you to think it offers improved security, then the site owners should take responsibility for any failure of their security and indemnify their customers.