Jackie,
Just watched the CCTV film of your caravan being stolen and it made me feel sick inside. It's something we all dread.
When we're not using our caravan, it's stored on a secure site with swipe card entry and cameras cover the whole site. The owners house overlooks the storage site too. We put the hitchlock and wheel clamp on and the caravan alarm on.
Before a trip, the caravan is on our drive and the wheel clamp and hitch lock are put on immediately and stays on right up until we leave. When we're in and out loading it, we lock the door whenever we leave it and never leave the keys in the unlocked caravan while we go indoors. We've told all our close neighbours that nobody has permission to move our caravan off the drive (but tell them if someone DOES!) and to call the police immediately if they see anyone trying to take it away, even if challenged and they say something like they have permission to take it away for servicing. We also park an alarmed car (with detachable towball) across the front of the caravan, but as they say, a determined thief will take it and all you can do is make it as difficult and time consuming as you can for them. Scumbags!!