It all depends on ambient temperature and humidity when it comes to fan cooling. In a moderate climate, fan cooling is very effective even a standard 80cm computer fan will perform. Clip on fan is nicer but be careful with AC driven fan. Use 12v dc fan for safety.
In a hot and humid country like mine, cooling fan must be able to move a lot of air (loosely translated as noisy fan) to see a dent and top off water runs out very fast.