My wife recently became concerned about people being able to see inside her SUV and see her get home bag. So she decided to do something about it. With a little help she got a piece of plywood cut to match the floor in the rear area of her vehicle. The board was then covered in carpet that matched the interior of her car. Four legs were then placed under the plywood. When the plywood is in place and the rear door is open you have access to a compartment under the plywood. If you look into the rear compartment with the door closed, it looks like it is empty.
It is a fairly simple idea that decreases the likelihood of your vehicle being burglarized