I used to run one of these "hidden antennas" in my Coupe.
I had mounted against the roof, hidden behind the headliner.
It worked, but not nearly as well as the stock power antenna worked. It would only pick up the strongest local channels, and even then it was static-ridden.
My
.
It may have worked better mounted to the glass, but I just wasn't happy with it. Reinstalled my stock power antenna, and haven't bothered with it again. It's still in the roof.
