So I crawl under and there is access panel in the very middle, a few feet behind the rear axle and just in front of one of the generator gas tank. I take the 4 screws out of the panel and low and behold, there is the censor. Is there supposed to be 1 in the rear, in the center... or 2, on each corner?
They at least built a wood frame for the sensor that it's mounted to, but it's flimsy and other than the frame being connected to the metal frame, where the sensor is, it's only supported by the plastic underbelly. So it can easily bounce around... here are some pictures.
Looking to the right and left of what else is under the plastic underbelly
Pictures back at the hole, the phone camera was just in front of the rear axel