As you have read in this thread, nobody has yet posted any solid, reliable evidence that VG's work at the end of a hatchback bodystyle to improve fuel economy.
I tested airtab style VG's , A-B-A, on both a sedan and minivan and could not detect any change in fuel consumption.
http://ecomodder.com/forum/showthrea...fect-6381.html
http://ecomodder.com/forum/showthrea...olla-2390.html
I wouldn't bother with them, except in very specific circumstances (eg: sedans with steep rear glass and short deck lids).