third brake light

I'm getting paranoid with all these SUV's running around. Am contemplating adding a third brake light to my '85 Carrere coupe.
Has anyone done so, or have any opinions on the esthetics of such an addition?
I've seen in a catalog an after market light that goes on the inside of the window (at the top, I suppose) but the footnote indicates it requires a removal of the rear window! There are two others offered that mount on the engine lid that are similar to the ones I've seen on later model porsches. Or should I get a Porsche part designed for a later model?
Does anyone out there have any opinion or can they refer a good source for purchase?
Thanks. jlex.