Vehicle to vehicle in caravan type runs, that'll work, long distances not so much as it's also very directional mounted there..
I had a short steel whip mounted on the DS corner of the rear bumper mainly used for communications bewteen myself & friends while driving somewhere or on the trail, but it didn't get out nearly as far as it should have and was very directional to that side. I kept ripping it off on trails, so I got rid of that and just using a magnet mount K40 whip on the roof. HUGE difference in output & receive range just with that location.