I thought the offroad dust would be bad news with the fan cooled bulbs. I am using "Vplus X series" LED bulbs, have been for almost a year. The color temperature is a bit high for my taste, 6500K, but they sure light up the road and I needed better lighting.
There is another style which uses copper braid heat sinks I am also interested in. I am considering some for the bikes, have not decided what to get yet.
-Joel.