Blas
Here is the reason that I grounded my filler cap. I have a fiber glass sailboat equipped with a small diesel. When I had a survey done a few years ago for insurance purposes, one recomendation was to ground the metal fuel filler cap. I knew this was rediculous as there is virtually no way to ignite cold diesel fuel with a static spark. Nontheless, I did this since it was recommended in my survey and I didn't want the insurance company to have anything to complain about.
That got me thinking about the metal filler on my fiber glass Cobra. Since the Cobra is fed 94 octane, not diesel fuel, I thought that it wouldn't hurt to ground the filler cap.
Wayne