A tail-light install sounds interesting. Side view mirrors are too far forward to help with my (perceived) problem. Drilling holes in the hatch or sail panels would not be my preference (to put it mildly!). Something hanging out the back by the rear license plate is the default, but I'm hoping for something a little more elegant. Hmm, maybe built into a rear spoiler....
I've worked with some production equipment that used a dual prism setup to achieve split vision with one camera.... I'll have to look thru our equipment bone pile
The problem with any warning device is... how to put it... people here are too stupid, self-absorbed, distracted... you name it. They'll be texting away, run into you, then swear it was your fault (hard to dispute if you're backing out of a parking space). If you don't have these problems where you live, then color me jealous!