This fuel box is a stock part for the Turnigy Trooper Nitro 4X4 SCT even though you can't actually find this in the parts list for the Trooper. You will have to buy the O-ring set for the Nitro rumble which if you compare the parts number, is the same as the Trooper.
The O-ring is used on the support post of the fuel box to absorb excess vibration from the engine and you have another larger O-ring for the lid.