Gee, if the roof is resonant on any band of interest, it might detune your antennas. Or it might make one antenna more directional than it already is. But, a roof mounted vertical would get the added benefit of a nice groundplane. Best Regards Dan Schaaf K3ZXL www.k3zxl.com NOBSKA www.nobska.net Cape Cod Instruments www.gnm-inc.com