Not sure who this is directed to-- but I suggest: 1. Insure the trailer for theft (the contents are a question mark and that is discussed on another thread). 2. put a padlock in the hitch closed with safety chains also locked and unusable. 3) leave the lights on outside and radio blaring inside. 4. Stick a bunch of crap under the trailer and the wheels. 5. Fake sign "video camera on site" ( I don't have that one yet) or real video camera. There are other more aggressive things I have seen on other posts.
If someone wants it, they can still steal it, but it would take some thought and effort. Theft risk exists for everything.. Why steal a $4000-$6000 cargo trailer vs any other thing--like a $20,000 camper. T