about 9 years towing our Jeep Liberty, no issues, (SO FAR) had a big nylon brush type guard on the last rig, it maybe kept some stuff from hitting the Jeep. The new rig has a rack guard, again, so far so good. I'll agree that maybe being a bit taller than a car has a lot to do with it. Maybe it is just luck.
I have towed four different vehicles with the only protection is the rock guard that goes all the way across the back of the coach and I have never had any damage on any of the four I have towed. I towed a Ford Ranger, 2004 Honda Pilot EXL, 2014 Honda CRV and now a 2017 GMC Terrain.
I can't speak on the Kar Guard and I have never used protection but I have pulled a jeep across country several time with no damage. I attribute this to the fact that Jeeps generally sit higher than most vehicles. Haven't done Alaska yet, so that might be a differen't story.