My take on this. The first is location. If in tweaker central, no amount of security is going to help.
Second, for a trailer, I secure it three ways:
1: I use BAL X-Chocks, and padlock them. This isn't "real" security, but it is obvious from someone on the side that the trailer is not going to be moving.
2: I use a security chain and high secure Abus padlock between the wheels and into the frame. This is where my real security is.
3: If I'm parked at the storage place, the owner let me bore a 4-5 foot hole, sink a chain in cement, leaving a few feet above ground. This gets secured to the frame via another high security lock.
4: Just to let potential thieves know that the trailer is secured, I stick a tongue lock on. Most thieves can bypass it, but it does show them that they are going to have to power up their angle grinder before they can leave with their prize.
This doesn't protect against break-ins. Here in Texas, if someone doesn't make the vehicle move, burglary of a vehicle is highly likely to get someone a night in jail, not much else. The only real way to protect against break-ins is to store in a good area.
So far, I've had good luck. The only thing I've ever had stolen was a used sewer hose from my real bumper.