Computer fans are made to cool a computer not a 250 watts. A bathroom fart fan pumps 80 cfm . Top Secret heat rises so put intake at the top of the space . With the vent at the top normal heat movement will help solve some of the problem. Use a attic controler to the fart fan. $13-20 bucks at a dyi. Temp controler is about 30 bucks.
Wooops forgot besure to use a intake filter on your system, no need to suck mites.