That's usually why enclosures are better as a once in a while access option,
If you want to leave the enclosure on everyday and Indexed a better model should be used no special wiring necessary,
Your attempting to use the existing enclosure in a way which it's not designed for,
Although some models do come with other connection cables/ rigging a fan into the existing wiring could risk low voltage to the unit where data is saved,
So if the Fan in question has it's own dedicated power source/ adapter it's not worth messing with.
But for the most part the fan it's self does not have to be inside the unit/ only accommodated or mounted on top and cut a hole in it to Pull air through the existing venting holes.