Put anything of significant weight inside and a serious frontal collision might end in some sort of safe induced head and neck trauma.

Mid nineties, I was filling up my truck at a highway service center, there's a cop about a hundred feet away standing outside his cruiser staring into the back seat and talking on his radio...as I was walking by heading to the cashier I look into the back of the Crown Vic and the rear seat looks like it had exploded, yellow foam bits, shards of puke proof cop seat interior and some random sharp pieces of sheet metal...and a safe...it was about the size of a plastic milk carton.

Now I'm standing there as well, mouth a gap staring into the cruiser, cop says..."that was the damnedest thing, we caught the guys that took the box from the Mini Mart, I was on my way back the house and hit black ice, I went around once and when I came out of it I was pointed back in the right direction, the car stopped short and the box came right into my back seat!!