I do not want to press you on this...
I can probably cut the hole for a 120 outlet and route the wire with its inner 3 wires (+, -, gnd) around and down to the power center. I just do not know where to attach them in any openings on the 'bars'.
I do not speak the lingo of the wiring into the 'bars' and their fuse-circuit setup. I have once gone there to tighten all the connectors per RV.net advice, and I probably need to get at this again.
Can you easily show a pic indicating where the three wires need to connect to create this new circuit?