Do I need a separate enclosure for the Power Meter?

No, you do not need a separate enclosure for the meter.  

The power meter can act as its own UL Listed NEMA1 enclosure when mounted in a protected environment.  If the meter is installed in an unprotected environment that’s exposed to the environment (like rain), it should be mounted in an appropriate UL Listed NEMA4 enclosure to prevent damage or hazardous operation.  In this case, Setra can be contacted to provide a NEMA4 enclosure kit including DIN rail mounts.