Anything locked, out of view, in the trunk is at least 100 times more guarded than something left in plain view inside the car.

My first empeg was a replacement for a stereo theft where they got the subwoofer out of the trunk despite the fact that the stereo was a removable faceplate version and the face had been detached. So out of sight in the trunk doesn't necessarily mean it won't get taken.

Although they didn't take the amps hidden under the upholstery, that was good.