Fuel Filler Grommet

So after pulling out my old rusty crusty gas tank and getting all the correct lock rings gaskets and grommets etc I'm ready to throw it all back together. Knowing I'll need some kind of lubricant to put on the fuel filler tube and rubber grommet/gasket, what should I use that won't react with the grommet or the gas should some get into it after install?

Thanks