In my 2005 19' International, the solar prewire ran from the 12v
electrical terminal block under the front dinette
bench seat, back along the roadside behind the kitchen, up through the closet into the ceiling, and ended coiled up in the ceiling between the air conditioner and the front vent. Access to the coiled solar wires in the ceiling was made by removing the front vent trim panel and searching around through the insulation.
Generally, solar installers recommend using heavier wire then what is provided by Airstream's factory prewire. However, in my case, the solar company (AM Solar) concluded the factory prewire would be acceptable due to the relatively short solar wire lengths
in the design of the 19' International and my relatively small 100-150 watt panel system. As a result, I used the solar prewires and just followed the factory recommended wiring layout, which made the entire installation much easier.
Good luck with your project. Solar has really worked out well for us.