One of the things with the series 59 style, is on my rig they fill up with dust during my hunting trips when I travel dirt/gravel roads for miles on end, and during the colder months I've seen moisture get in the lens, and over time, the sun fades the lenses out so the color is less visible...
so I ended up going this route, which is a totally sealed LED unit:
http://www.ledtrailerlights.com/cm/cm_M23015.htm