One method that I use in my car in order to prevent stuff from my boot is stolen.

1. I change the current lock in the boot to SOLEX or another type of Locking device
2. Disable the boot opening button inside the car

One thing that these stealer and robbers dont have is time. Cause time is risk for them. I always carrying my company expensive electronics measurement device inside the car, and this method at least has prevented those car breaking crime that always happen in my neigborhood.