Here's the very best carry solution for a FS spare:

http://www.vehicross.info/forums/showthread.php?t=18343

Carry it vertically upright in the right-rear location of the cargo area. It minimizes cargo area impedance and diagnolly counter-weights the driver sitting in the driver's seat. In addition, it maintains the clean aerodynamic's of the VX (good MPG) by not having it on the roof as a wind-catcher and doesn't tweek the rear door hinges over a prolonged period of time if mounted on the rear door.