For vehicle use, a small magnetic-mount antenna on the roof will make a big difference in effective signal strength. I don't know the exact model of the one I've got but it's similar to this:
https://www.gigaparts.com/mfj-1722.html
Just make sure it's matched to the frequency band you're using.
You can get more gain with bigger antennas but they're more of a hassle if you're travelling with your gear or constantly mounting/dismounting them.