If yours is like mine (Arctic Fox 27-5L), that separate box in the cord storage area is part of your generator prep package. Mine runs from there to a junction box adjacent to the front storage compartment (under the overhang) where a generator would be installed. The idea with mine (and probably yours) is to install a generator to output its 110V AC to the the adjacent box which is wired to the 30 amp receptacle box in your cord storage area. When using the generator, you simply plug the shore cord into that 30amp outlet - thereby energizing all the AC outlets in the trailer. Think of it as a big extension cord from the back to front of the trailer.
In my case, I don't have or plan to get a built-in generator. So, I hijacked that wiring and connected to the output of my solar power system inverter. When I'm dry camping, I simply turn on the inverter, plug the shore cord into the 30amp receptacle in the cord storage area, turn off my converter and microwave and set the water heater and fridge to gas. The inverter energizes the AC outlets in the trailer.
If you can get your 2nd AC wiring to the would-be generator j-box, then maybe you could build another shore cord to plug into the extra receptacle in the cord storage area. That cord could be dedicated to the 2nd AC. I would add a fuse or breaker of appropriate size (30amp). You would only need to plug that second shore cord in when the 2nd AC is needed.
2020 Chevy Silverado 3500HD Duramax 4x4 Crew Cab Standard box
2011 Arctic Fox 27.5L
