How important is a rock shield when towing a car?

Four years and 20,000 miles towing my Mariner behind my Winnie View. No rock shield and no damage. I tow some on unpaved roads here in Arizona, but not too much.

I have mud flaps and the rock guard across the back. I have had no damage from rocks. Make sure the rock guard is at least 4" off the road. I also never drive on gravel roads faster than 35 mph.

One road we went down was gravel that was fresh and they had used it for construction equipment. Blew out all the lights on my wrangler and had gravel on the bumper. Only time in 350 k miles.

I think we've had one semi-serious rock strike in 11-towing years and that wasn't a rock...it was a small piece of rebar that was kicked up by the rear MH tires that imbedded itself in the lower plastic bumper of the toad. no rock shield was gonna stop that.

On a rainy driving day on an interstate and for lack of something creative to do, I did a survey and watched motorhomes with rear rock guards as they passed in the opposite direction. On those with guards, the road water was splashing high onto the hoods of the towed vehicle. The ones without a guard, the water spashed low at tire level. It convinced us.

I towed our CRV for 60K miles without a scratch until I reached the Alaskan Highway! This is what I then learned about toad protection from rocks.

The worst device is the vertical shield mounted on the car. These hard shields can and do reflect rocks back to the motorhome and can and will cause paint and even rear radiator damage. Adding some type of damping material to the front of the shield will help reduce rock reflection. A full custom fitted bra on the car will protect it. However it must be washed every day to remove the dirt and grit that will get underneath and scrub the paint. The best device for protection is the horizontal shield type of device that extends from the motorhome to the toad. This will not however protect the toad from rocks when meeting or passing vehicles.

The toad radiator also needs protection. The horizontal shield that installs above our CRV tow bar would not protect the radiator that is below the tow bar.

The worst device on the motorhome is the large rear mud flaps installed at the rear bumper and are less than 5” from the ground. These mud flaps will kick up rocks to the toad. Actually these aren’t mud flaps at all. They are a marketing and advertising device and not intended as a mud flap. If yours is less that 5” from the road then remove it before the trip. The broom type of mud flap will also do little to stop rocks.

Had more damage with a rock guard or brush than without.
When they hit the road. They kick up more stones and dirt.

Just plain old mud flaps work the best.

We've towed our Jeep Liberty to Alaska and have full-timed with it for 10 years including boondocking along gravel roads. We have had no damage to the Jeep from rocks.

One other thing, we have stiff flaps behind the MH wheels but we don't have a rear stiff flap. We actually saw folks along our Alaskan trip removing those stiff across-the-rear flaps because of rocks laying at the base of the toad's windshield.

Ours shield shows a lot of scuffing and dings from rocks etc. A lot come out from under the Mh and flap and tumbles over the shield and onto windshield and roof etc of towed. the front end of car is 100%.
They work but I don't think they design the locating or shape according to test behind a MH with a mud flap and or rear radiator, for sure.
The one that goes on the bottom of the tow bar seems like would be more protection for towed but I am not sure. It might be just better, for parts of the towed. Both together?
Some kind of diverter mouldings, or whatever on the rear, of the coach seems to be in order. The tublence behind MH is huge. Any oil seepage etc, and rocks can end up on the top, of coach as well as roof, of towed. I you smell oil blowby it could be becaause fumes are being sucked up to the top, of coach and into rear camera opening.
The shield works to a large degree but we still have to clean the car from being towed

I towed a car on a dolly for a lot of miles without rock damage. Several years ago, I bought a mudflap that goes across the entire rear of the MH. The only issue I had was muddy water thrown on the toad on the dolly.
I now tow a pu 4down, again without a shield except the flap on the MH. it seems like there is less muddy water thrown on the windshield and never had a problem with rocks.