I'm not a fan of fans because they make noise, consume power, collect dust, wear out. 

The USB modules get warm in normal use, and very warm if overclocked.

I bolted the modules on bits of metal from my scrap box, with CPU thermal paste.
Zero cost, silent, and the modules don't get hot.

Unit 1 - an aluminium heatsink from a scrapped PC PSU:

Unit 2 - a milled aluminium case from a old project box: