On my 2014 FC 20' the solar pre wire is under the bed (which you located). The upper end is found by taking the trim off the front Fantastic Vent. Mine terminated there with about 18" of extra wire.
Because of clearances, I had to drill up from the bottom through the metal and the flange of the Fantastic Vent to get the wires out through the roof. I sealed them well with Dicor sealant and then sealed a 90 degree elbow designed for flex conduit over the top of that. From there I use flex conduit to my combiner box which I located under one of my two 100 watt Grape solar panels which I got from Costco (unfortunately, no longer available). I was able to fit one of the panels between the AC and the Fantastic Vent, and the other along the road side roof, long side forward. They make an L arrangement.
The interior wiring went to a Blue Sky MPPT charge controller mounted on the wall between the dinette and the foot of the bed and then connects to the other electrical systems under the bed. As there is nothing but one flashing light on the charge controller, it could have been under the bed. I use a Tri Metric meter to monitor all 12 volt
power in my unit. I understand that Blue Sky has a similar monitoring system, but when I ordered mine, I was unaware of it, and was already familiar with the Tri Metric.
It makes a good system, especially when combined with a new Progressive Dynamics converter/charger section in the power panel. In the spring, I intend to change to a pair of 6 volt golf cart batteries in series to replace the two type 24's that came with the trailer. I will have to raise the cover of the battery box about an inch to do that battery change.