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.