I have been trying, experimenting with HF mobile for many years and I have tried several different antennas.

I recently bought this Alpha Moto HF antenna from Alpha antenna. I use it with my IC-7000 and a LDG tuner. The antenna is mounted in the center of my folding, aluminum tonneau cover, near the back window of my truck, not the best spot but it is ok. This antenna works. I have never really had much luck with 20 meters mobile.

I installed the antenna and parked in my driveway I made several contacts on 20 meters across the USA and some DX. This antenna hears pretty well, it will not bust any pile ups but it is short, 5 feet, fairly easy to install, plus I can park my truck in the garage, whip is very flexible and it has a spring. This antenna covers 40 thru 6 meters using a tuner. Other base loaded antennas I have tried did not work well but this one does. Lately upper bands have not been open when I am in the truck but it should work ok.

WM3M