DNP3 Comms to S7 300

I have a potential project using some RMUs using DNP3 communication protocols.

The project has been scoped to use S7300 plcs so I need a way of getting the data from the RMUs (DNP3) to the S7 300 plcs, preferably over Ethernet, but could if necessary go to Profibus.

Has anybody used DNP3 on an S7 300 platform and be able to point me in the right direction with what hardware and software might be required.

For hardware how about:

http://support.automation.siemens.com/US/view/en/46635650/133200
http://support.automation.siemens.com/US/view/en/46636298/133200

Ok a bit more detail on this now. It seems that the PLC I install is to be the DNP3 master with the RMUs as slaves (supplier is Lucy switchgear).

From what our HV engineer is describing they are going to connect each RMU to a Modem (or common modem) that is then going to communicate with the 319-3 PLC.

Anyone any ideas on configuration of this kind of scheme?