Well, it depends. The antenna does not need a DC ground path to work well.
Inductive/capacitive coupling to an adjacent metal surface is generally
adequate. But there are so many installation specific issues that it is not a
simple answer. However, most people are unaware that one of the best antennas
for 2m is a 1/4 whip in the center of the roof. At highway speeds, the 5/8
whip bends over and distorts the pattern and causes a null in the forward
hemisphere. For stationary instances, the gain antennas may indeed offer gain
over the 1/4 wave. Just some thoughts...

73s,

Evan