Thanks to all.
Back home now with internet again (state/federal parks since the private Rivers Edge in Gatlinburg).
Light went out the next day, and I don't think we even filled the tank before it did. I checked the cap after your responses, so maybe that did it.
Interestingly, I accidentally left the cap OFF and dangling for about 10 miles a day later, and the light did not come on.
Had a great 2000 mile loop from Roosevelt SP (MS), Desoto SP (AL), Rivers Edge (Pigeon Forge/Gatlinburg, USA), Cumberland Mountain SP (Crossville, TN), Hillman Ferry Campground (LandBetweenLakes, KY). Followed by a marathon 600 mi return to Baton Rouge in a single 10 hr day!
23,400 miles now, with over half in the last 6 months, and really no major issues. (I no longer notice the squeaking now that it may be diminishing, I am getting accustomed, radio is on more, roads are smoother elsewhere). We did extensive touring in many parking lots with very good results. About 11 mpg average.