[68Timber]

One of these would be cool and accomplish the same thing:

http://www.ebay.com/itm/08-09-10-Challenger-Factory-Fuel-Cap-Chrome-Stock-NEW-/370609932880?fits=Makeodge|Model:Challenger&hash=item564a12ca50&item=370609932880&pt=Motors_Car_Tr uck_Parts_Accessories&vxp=mtr

If you got it from a junkyard with a few inches of body panel around it to graft in where your factory filler is, it wouldn't be so bad.