A master blaster would definitely do the trick. I inadvertently set one off last week when working on someone's shed alarm... Nobody would hang around for long near one of them!Following on from Duane's post , Put a Master Blaster in from an inverter, controlled by an alarm in case they get into the front of the van. They will not hang around in close proximity to that. There may be a 12v system that is just as loud now.
You could also disable the front locks , but that could turn out to be a pain.
Sent from my SM-G920F using Tapatalk