We have the Leece Neville alternator with a smart reg on Elyse ...twin belt pulley...and no dust...and the belts are fine after years.
Previous experience with this leads me to believe that the pulley is the problem.
You don't need much of an imperfection in the pulley groove to lead to belt destruction.
The belt should be sitting in the pulley groove, not bottoming out and the faces of the pulley groove must be absolutely devoid of any corrosion or dirt, anything.
Ours has worked perfectly for the last 6 years ....and the big advantage of this setup is that the 2 belts on the LN 175A alternator are the same size as the belt on the small alt that charges the start battery.