I agree with Sol on this one. Fans small enough to fit in a single-drive enclosure will not work well, will be noisy and will fail quickly. One option is to get a multi-drive enclosure that is larger (and consequently has a larger fan). The other option is more of a home-brew; Use a Zalman heatpipe cooler to increase the surface area (I've had really good results with these), and then mount a larger (>80mm) fan somewhere in the vicinity to get some airflow past the drive.