Do you follow the other threads in Aerodynamics? This is kach22i's latest post in the smoke and wind tunnels thread:
http://ecomodder.com/forum/showthrea...tml#post564458
It appears there is an underbody tunnel to the height of the axle line. What is it's width? Could you group the batteries in between the wheels on each side, in a catamaran body for less frontal area.
The fan could pull 10-15% of it's flow off the top or sides of the tail to eat any attached turbulence at the last moment before it's added to the wake.