It worked surprisingly well for only 2 highly mounted sensors. Straight back, you'll get the first faint beep starting at about 3ft-4ft that turns into a solid beep at about 1ft. At 45 degree, you should really stop at the first few beeps.

I don't recalled what size drill bits I used, but I did start out with a small drill bit (probably 5mm), then step up to a larger sizes to enlarge the hole until the rubber grommet fit in tightly.

Again, the most difficult part of the mod would be to fish the wires through the rubber boot between the tailgate and body. A couple of others that also did this project also agree...so don't say I didn't warn you