How about something like Cody's layout number 1 (direct driving the center wheel, chains fore and aft) except instead of using one motor you gear 2 motors together like
this
The setup shown has 4 "wheels" per side, with the fore and aft wheel driven by the belt; you could do the same thing with 3 wheels and chain, using the center gear to drive the wheel rather than the 2 outboard gears.