I've not had the experience of carrying high value cargo, and, I'm not going to directly answer your question. But, a look at the philosophy of break-in prevention may be in order. First, any additional locks, visible window grills, and maybe your ad-wrap or signage are going to advertise that there's something inside worth stealing. Second, a criminal attack on your new physical security features will probably cause more damage to the vehicle than garden variety break-in. You may have to weigh relative values of your cargo, against vehicle damage, against insurance coverage and costs.