I have a Nissan cargo van with a 6 inch factory antenna. I have still not yet bought the $150 service manual, so i'm not sure if the antenna has a preamp or not. But it does just fine for AM band DXing.

Decades ago, i saw in Wireless World magazine ( UK ) a project for a car antenna that used two ferrite bar antennas at 90 degrees to each other. Some kind of phasing ckt ruled out voltage cancellation. Thus a mobile magnetic field antenna with no nulls. I wonder i saved that article somewhere.