This shape is a low drag glider fuselage similar to the Morelli/Aperta profile. The Motorcycle/Scooter threads have some excellent discussions. Looking at your top view we want to use a 3:1 L/W or longer symmetric airfoil section. The typical max width on a motorcycle is 26 in. at the handlebars. If possible the lower battery boxes should be as far forward without contact the feet. Reducing ride height and the gap between a rider's back and the tail are critical.