Many people use marine compasses in their vehicles. They are handy for off-road activities and driving at night, where it’s easy to lose one’s bearings. Mounting a compass in a vehicle is much the same as mounting it in a boat – remembering that deviation from surrounding magnetic sources I likely to cause issues.
It can sometimes be difficult to find a good mounting position in a vehicle because of all the gadgetry close by. Take your time to test potential locations and manipulate sources of deviation so as to ensure that you don’t miss an interference that isn’t noticeable when the car isn’t running, for example. Test things like car stereos and portable speakers as these are known to affect compasses.