Larry,
I think the most popular option is to install a spoiler on the rear trunk lid with the integrated modulating brake light. There are a couple of advantages, IMHO. First the light is at eye level and should be better at getting their attention. Second, the connections are made insde the trunk lid so it is easier to work on.
Some of them, I think Electrical Connections, also can act as a turn signal in that half of the bar will flash as an indicator.
The only real caveat is if you already have a lid munted rack. It may be in the way. If you don't already have a lid mounted rack then this is the way that I would recommend you go.