Hi Colin,
I suspect their explanation why they cannot use security cameras is wrong.
Many places, both public and private have security cameras.
We have one on the main entrance to our apartment block and several in the basement garage area. Shops, banks, and similar establishments also have them.
I would try asking the asking the campsite for the complaints form re the security cameras and also maybe for them failing to take reasonable care of their customers, and see their reaction .
I was told by a Spaniard some years ago that shoos and the like must care to protect their customers from dangers including being robbed. I do not know if that idea is supported by the law.