We have the Defender. We still end up with a spray of small rocks and dirt or anything else on the road on the col and the roof etc.
The problem is the giant vaccuum behind the MH. The Defender keeps it off the front and most of the hood but the air from the rear radiator and from under the MH especially tumbles over it.
Some say removing the flap under the MH will help with the problem. I've even though of extending the distance between the MH and Toad.
We use the Sterling tow bar also. It ends up very grimy too from everything being kicked up or sucked up in the rear of the MH.
It would seem Roadmaster or someone would have done a study of what to do about the problem, rear radiator or not on MHs. I think most pull up a lot of dust oil and rocks between the MH and Toad???
Shouldn't be too tough for them to design a shield to stoop this.
Maybe we need both devices?