This information is mostly for Eastern countries (former USSR) though many options are applicable everywhere. Security is split in to parts: day and night
Security during the day
Almost 100 percent assurance is given by an insurance. However, when travelling in the foreign country, insurance companies often wouldn't sell their plans to foreign plates cars. Even if they would, comprehensive insurance is extremely much more expensive in comparison with the regular insurance. This is in Eastern countries (former USSR) unlike the US. Nevertheless, if possible it is always better to have the comprehensive insurance rather than not to have it. It is better to choose big and long standing insurance company because small companies are known to disappear from the market on a regular basis.
Steering wheel locker
Choosing parking space
Security during the night
In general, at night the van is more secure because someone is inside of it. I mean someone is sleeping inside. I mean I am sleeping inside..
Thus, merely theft is not possible without notifying me about it. So the only option for the criminal is forcible theft I. e. assault. So the criminal needs to forcibly kick me out of the truck to take my truck. Assault is much more serious crime than a theft, thus penalty for this felony is extremely serious and hard in most countries of the world. Hence, this risk is much lower than the risk of theft.
Nevertheless, nothing is impossible. So there are still some ideas to prevent the bad from happening.
Turn on white lights
Most trucks have white lights on the back of the cabin, on the rear bumper. They can be turned on for the whole night. So everyone knows that someone is inside of the car. Though these lights consume less power than the front regular lights, we still need to take care of the car battery. Setup solar or have a jumpstarter in the xarin case the battery drains during the night and in the morning we will not be able to drive.