I was looking at connectors & came across this...shows an interesting way moisture can creep into your enclosure---even when you think it is all sealed up with top-dog waterproof grommets!
http://www.dsmt.com/products-and-services/moistureblock/
Wicking draws up liquid through the interior of the power cord, bypassing any exterior seals and bariers [sic].
DSM&T has created and developed MoistureBlock® Technology to stop water, oil and other fluids from migrating in either direction through a power cord, preventing damage to involved internal circuits.
This patented process adds additional protection from moisture by sealing the conductors at the micro level –down to the individual copper strands themselves! Ensuring your product is protected from the elements.