Could you just hide a phone in the trailer and use a GPS tracking app such as this? Any time the phone came within range of a cell-phone mast you could get an alert plus location data.
A good friend of mine did this. Her husband was screwing around and also bankrupting them. She downloaded an app on her husbands phone so she could track it. Seems many of those late at office and "something came up" were bars and girlfriends. She could nail his location within a few feet. The phone did not have to be active either. Long as it was on. Using her phone she could nail his location anytime. He never figured out the app was on his phone. All you need is a phone with an extended service battery and a way to secure it out of sight and out of mind. Of course you are paying for the service but you know where your stuff is including wayward husbands. Then there are things like LoJack but you need to call for cost details?
Ron