My RV mounted PV panels are basically flat and travel many dusty roads. So they gather a lot of dust and are difficult to clean. They generally have dust/water marks caused by light rainfall. I found a few interesting scientific (non-commercial) threads about hydrophobic and/or hydrophilic chemical coatings that may assist keeping PV panels clean, plus that RainX should not be used.
Does anybody have further information or vendors that do this?