Id say most of us have them. It's cheap insurance if you're on the trail at night. Check out the Mauser build thread. He put them in clever places.
These are mine, pretty simple.
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Hijacking Kyles Thunder, but this is mine with the same lights on a 2 dr, just 3w...
I stole the idea from petey, also check his build thread. He has them in green.
The reservoir helps cool things down. The cycle of the shock going up and down creates heat and the reservoir provides more surface area to cool it. Shocks will fade if they get too hot.