@brianwilliams - You are correct in your understanding. If you move your LAN connection to the switchports, you will need to configure VLAN interfaces instead of ethernet sub-interfaces as you did before. Simply set one of the switchports as a trunk. This can be done in the web GUI, by navigating to the "Ports" page and changing the mode from there, or in the CLI by going into the "interface switchport 0/x" command set and issuing the "switchport mode trunk" command.
Keep in mind that NetVantas only support 802.1q trunking encapsulation, and that the device terminating the other end of the trunk will need to have the same encapsulation. Also, by default, VLAN 1 is the native VLAN unless otherwise specified.
Let us know if you have any other questions.