My "1984 Airstream Trailer Service Manual"
clearly shows valance lighting. There is a switch behind the curtains on the road side of my 1983 Excella under the speaker near the lower curtain rail to turn on the "indirect lighting". Everything was wired in and obviously factory, although only 1 of 3 still worked.
I don't know about your year model, my 1967
Trade Wind does not have this.
My plan is to replace the original ThinLites with the bare tube fixtures from Backwoodssolar.com. Scroll down from the RV fixtures at Lighting
Since they are behind the valances, a cover is not needed. Plus, they use regular 24 or 48 inch tubes vs. the smaller ones.