I don't know if it's the best fuel storage container or not, but I've used a 1 liter metal Keytone solvent container that has been drained & flushed with a bonding strap attached to it. It's small enough to fit in the panniers/tail bag, where it won't take up mich room, the metal containers are generally built strong, almost crush proof and they're chemical resistant.. Just make sure to have that bonding wire attached when transferring fuel to dissipate static electricity.