Answer
WJ-NV200 Does Not Support HDD Expansion Units
The Panasonic NV200 recorder does not have the extension slot connectors in the back for the Expansion Units to connect to. Only onboard storage is available, 2 x HDD slots in the main unit.
If Expansion Units are required, the WJ-NV300 recorder does have the capability to connect up to 2 x WJ-HDE400 units