I drive a motorhome and flat  tow a Suzuki Grand Vitara behind it. I tried the standard stone /chip guard mounted on the Tow "A" frame. I found it was a waste and didn't do the job well enough.

I then made up a full width mudflap under the rear of the motorhome. Found a place on the chassis to mount two steel bars 20mmx 5mm with mudflaps across the whole width of the MH. I used some Plastic mudflats made for trucks that have anti spray on one side and have found that not only stops the stones flying it also keeps the Suzuki much cleaner.

I have adjustable airbag suspension on the MH rear so made them to fit with ground clearance when the MH was at it's lowest setting.

Less than $150 all up for parts, except I had the metal bars hot galvanised for longevity. I think that was $80.

I will add some photos if I can find the camera.