Dave:
No place is too small or insignificant! No, I wasn't there for the dunes. I went on line to see where the nearest RV supply to El Centro was located, and there were two, both tiny, in Brawley, so went for a drive.
I have since found another store, even smaller, in Indio. I didn't check there for the outside light, as I already have that, but I doubt you would be disappointed if you shop there.