Hello,
This is totally possible, though there is no official guide, thus, I will try to demonstrate by performing a local configuration. Configuration is relatively simple. For a serial device I client application I used Hercules.
Below configuration is performed on TRB145 device with 7.03.4 firmware, however, configuration with TRB245 is identical.
To begin configuring, login to TRB245 WebUI, navigate to Services -> Serial utilities -> Over IP. In Over IP mode, device operates as a transparent gateway, simply providing connection between end nodes and forwarding anything that is passed through serial interface without any data formatting.
In the configuration page, Add a new instance for RS485 device

In the device configuration window set the following:
- Enable
- Baud rate
- Data bits
- Stop bits
- Parity
- Full Duplex (if used)

Next, set Over IP settings:
- Mode, set as Server, since I assume the device will be located in some remote location and will have a static/dynamic Public IP, witch is needed for connection.
- Protocol
- Port
- The rest can be left default.

In addition, you can limit the hosts, from client connection can be made by configuring a filter.
Save this configuration and test it:

Best regards,