Chris is right. The only time I have experienced problems has been with heated windscreens (freelander and mondeo), but the use of an external aerial sorted it out properly. Then again, my system is PDA based, and it's receptive capabilities are a tad, well... rubbish.
Try it on your dashboard first, then if it doesn't work, you could always (and I am not kidding) protect it with an old tupperware or something along those lines.