Here is the system direct from Roadmaster. Their latest Guardian model below with a description:
Protect Your Towed Vehicle and RV Against Dings and Rock Chips.
The Guardian is crafted from rotationally-molded, high-impact polyethylene to absorb the impact of rocks, gravel and road debris — instead of ricocheting it back at the motorhome. The Guardian can be attached and removed in seconds, and fits all ROADMASTER tow bars equipped with quick-disconnects. Can also be used with a tow dolly to help protect your towed vehicle by using Guardian bracket part no. 2000-8.
If you tow more than one vehicle, the Second Vehicle Kit has all the mounting hardware necessary to swap the Guardian from one vehicle to another.
For maximum protection, use a Tow Defender and a Guardian. Motorhomes kick up rocks, gravel and road debris, but so does oncoming traffic. A Tow Defender/Guardian combination protects your towed vehicle's finish, headlights and windshield against damage from both lanes.