Yes my Interstate came with Mercedes factory roof rails. I think Airstream dropped them from newer models, probably to save some cost. I used Rhino-Rack cross bars attached to the roof rails. I did it to raise the panels above the bath vent. I also replaced the gray tank vent with a lower profile version to the 360 Siphon vent cap.
But there are other ways to mount the solar panels on the roof. I'd use the AM Solar mounting accessories if I was doing this again. See link below for details:
Thanks for the link. I am going to add panels. Looking at different methods to best utilize the limited real estate.