Any field disturbance sensor should be mounted facing up; the field it creates is a "dome", so it will cover everything above and to the sides of it. There is no reason to mount them sideways and doing so will only reduce the sensor's effectiveness. The field does not penetrate metal at all, but is unaffected by fiberglass and other materials. I mounted mine to the lid of my center console. I made a small ABS plastic box for it to fit inside, and routed the wires under the console. Since it's on the top of the center console, it rests right at the top of the tub level - this makes it very effective for topless season.