plumbstar

I placed my nav and xm antennas under the dash & they work fine. There is a plastic access panel on the top of my dash. I siliconed them to the bottom of it. The antennas will not work thru a metal dash panel. It also depends on where you place the antennas in relation to the windshield. I would get better reception on the roof but it has never been a problem. The xm buffer is usually big enough. My 2001 RX300 has the factory nav antenna under the dash. I hope this helps.