The company I used to work for twice accidentally brought illegals into the UK.
Both times, the illegals entered our lorries about here, when the drivers stopped for their breaks.
Our vehicles were steel-reinforced box bodies with a bulldog container lock
https://viperguard.co.uk/truck-trailer/bulldog-container-lock-1
the trailer was locked and sealed. After it's sealed, the driver isn't really allowed to open it up because it means the goods could be compromised.
On both occasions with us, it seems the gang forced open the door at the top, and got just enough room to allow 10 starving immigrants in through the gap. Even with the door locked.
Most of our vehicles were the same box bodies. The company next to ours had a much bigger problem with bringing in illegals as they were curtainsiders, and I think they must have brought in about 10 lots of them just from what I saw when they stopped at our depot and everyone legged it.
Of course, none of ours were fridges.