The rear of the Box Trailers could be fitted with an alarm on the locking bar at the rear of the Trailer Trt, this in-turn be wired into the Trailer's Lighting etc, the light Plug connects at the back of the Unit ( The Front End) the same could be done with A curtain sided trailer, the trouble with the curtain sider is the reinforced covered wire that runs from the front N/S+OFF/ Side of the trailer through the locking straps & meets at the rear of the trailer again into the locking bars, but they are that cute that they release the wire lock & re-connect when the Stowaways climb in, there is 2 ways to stop this, a seal clamp lock at the wire meeting point, some have started getting in through the roof of a converse sheeted roof, the same could be done with that trailer, the do use Drive through bays just like an EX RAY tunnel, but at the end of the day the problem lies with the French port or any port, they do not check the trailers properly, until that is done, they will keep coming.