Well though Trailer (And motorhome) theft is becoming more common. So are Trailers and motorhomes. When you looks at the PERCENTAGE of RV's stolen. I'm not sure the change has been that great if that is there is one.
Several things you can do to improve security. One is to chain it up.. A chain through the rim and wrapped around a frame member. Another is a GPS tracker device. though those can be a problem on a Trailer.
Next: Many PRIVATE parks have security.. I'm trying to get the park I'm in now to add a few things that will make it easier for the 24 hour security guards but (Cameras at the entrance/exits that can spot your tags. both park tag and license plate) this would also assist with recovery of a stolen trailer.
THey do have cameras in many areas... Short story I happend to walk past the manager's office and there were 3 people in there
Assistant park manager
Grandfather
Grandson
THe manager was showing the others a video
The Grandfather was not looking happy
The bicycle theft grandson was looking very contrite.
The sign next to the bicycle rack he was stealing from says THIS AREA UNDER VIDEO SURVEILLANCE.. It did not lie.