battery into jayco hawk

Hi guys, Look, I know this subject has been well covered by lots of members but I just need that last little bit of knowledge or advice thats out there.... before I go ahead and fit a deep cycle battery, plus CTEK charger if needed into my 99 Hawk outback.
So far I have found out that the stock Centaurion CS 2000 inverter/converter is a pretty average unit with almost no wiring information. The common theme seems to be to replace it completely with a multi stage battery charger? Is this necessary? Considering that is is working fine at the moment when connected to 240 volts?
After checking the back of the Centaurion unit, there is labelling to show where to connect the battery + and - wires.....however, the positive terminal connection already has a wire connected and this goes to a finned alloy regulator?or one way diode?device? that is mounted to the campers plywood floor right near the Centaurion. This thing is about the size of 2 cigarette packets and the positive wire then exits this and goes back into the main wiring harness. It is not grounded.
I have had a lot of 12 volt experience working with motorcycles etc, so im keen to make it happen but Im just not 100% confident and cant seem to get any technical info or wiring diagrams?
Any help would be appreciated!!