The Poron unit I got has a tone that gets higher in frequency the closer an object gets and has a female voice that says 8 feet, 5 feet, 3 feet, 12 inches, and crash. It is also accurate. I backed toward a fench and I thought I was going to hit it while the unit said 3 feet. I got out and darn if there was still 3 feet.
It was a bear getting the unit into the left top tool box. There is a small opening from the box to the rear of the wheel well about a foot from the tailgate where the left side meets the floor. Its easy to see from below the vehicle. The opening has a 1 inch by two inch flap to keep water out. You route the sensor wires through this opening into the bed of the truck. You can then push the wire under the left side plastic and using a coat hanger pull them through one of the drain holes in the top box. Tight fit, but you need to be patient. I also pulled power and the audio through the drain hole. I tapped +12 from the trailer hitch lead (there is a tag on the trailer wiring about 6 inches from the actual trailer connector that gives the color cose, I believe that the light green is the backup). There is a ground lug onto the frame below the left box that has a ground brain dangling from it. That is where I got ground for the unit. I ran the speaker wire down the side between the floor and the side, sort of under the side plastic and then through the midgate. I still need to clean up the installation, i.e. velcro the unit to the side of the top box and pass the speaker through to the cab instead of across the midgate gasket.
I installed one sensor under the center of the bumper above the hitch, and the other two about two feet on either side right where the bumper steps up a half inch. The unit comes with right angle brackets for the sensors sort of like a hinge. The sensors have a clear cover that can be painted. There is supposed to be available covers in matte gray but I have not ordered them yet.
Hopefully I can get pictures in the next few days to post.