Unbelievable. Cant believe what they will steel these days. Maybe an alarm would be a good idea. I just brought a mobile alarm from a company called Heidi Security. Works really well. Plus i'v found that because its mobile i can use it anywhere.
Hope you don't have any more problems with theft.
Recently I had my Horse box broken into whilst Hunting... Found this alarm online, has anyone tried this or any similar products? http://security.heidi-electrical.co.uk/sentry/