The SP5 PCD 2W will dissipate about 5 Watts when controlling a 600 Watt load. The type and amount of cooling that would be required when mounted inside an enclosure will depend on several factors such as the power dissipated by other equipment within the enclosure, the volume of the enclosure, the load that the PCDs are controlling, the maximum outside temperature of the enclosure etc. You need to insure that the ambient temperature surrounding the dimmer doesn't exceed 40 degrees C (104 degrees F). Also, any amount of air flow across the heat sink of the dimmer will go a long way to reduce its temperature rise.
If anticipating mounting this power pack in an enclosure, we recommend testing the worst case environment that you expect to encounter and perform temperature measurements at various points within the enclosure in order to determine if additional cooling measures need to be implemented.