One thing I did years ago was to build a narrowband preamp. carefully tuned
to my station. It boosted the signal strength of that weak station without also
amplifying stronger stations, which would have caused overload.
You might benifit from diversity reception. If you can get your hands on a
diversity reveiver (Nissan used them in some cars), install a second antenna on
the opposite side of your car your car. The receiver will select the one with
the strongest signal.
You might also see if you can tune your antenna to the part of the band you
are most interested in.