I agree with Tom and Lon on this one.
I have a presentation that I have given to several amateur radio clubs about theses parts. It's called the Wall of Shame. The photos in the presentation were taken at Dayton last year, and the year before. The installs are so bad, you can't believe they actually work!
One of them belongs to a rather famous (perhaps infamous) amateur. Even though I covered up the signage on the side, one amateur in Albuquerque, recognized the vehicle.
He then explained to me that this install was his second attempt. As the story goes, the first time he mounted the antenna, he used the brake light lens guard, which turned out to be glued on plastic, not metal!
There are a couple of the installs within the pages of my web site, but I have refrained from putting them all there. After all, some folks need their anonymity.