My experience with the GTO Judge spoiler (which is essentially the same) is that there is a gasket under the pedestals, but I will defer the expert opinion on that to someone who's got a T/A spoiler.
The outer edges of the spoiler also rest on the body with the trunk closed - no gap. If it doesn't, vibration and down force will cause it to eventually crack. It beats up the paint anyway, no matter what. It's best to localize it. I have seen guys add softer padding to the end plates, which they later remove for shows. (Some kind of urethane foam, if I remember correctly.)
