When thinking about vehicle security, you are better to start by thinking about what you are trying to be secure from:
1. Accidental or malicious damage to the vehicle.
2. Damage caused by break-in attempts, whether or not successful.
3. Theft of valuables from the vehicle
4. Theft of parts of the vehicle.
5. Theft of the vehicle.
6. Recovery of the vehicle after it is stolen
7. Catching the thief.
The reality is that each of these concerns probably has a different best measure.
When choosing the measures, think about how they will impinge on your everyday use of the vehicle:
1. Locks and clamps can be a pain to have to fit and remove for each journey.
2. Heavy metal security hardware could do you a lot of damage in the event of an accident.
3. Immobilisers are one more thing that can go wrong. Been there, got the t-shirt.
4. Alarms only annoy people nearby. They don't usually do any good.
5. You might not want your van back after it has been stolen and abused.