Just thinking out loud:
*consider a 2-D streamline form to minimize frontal area
*do the 30mm clearance at the front axle
*do the 100mm clearance at the rear
*this offset will allow you to use the entire under body as a drag reducing diffuser (no downforce).
*place the batteries just above the belly where you can to keep the C.G. low for roll stability.
*rake the body with low front/high tail.This will help keep the upper airflow attacking the body all the way to the canopy,where the flow will be compromised by the opening.
*place the canopy as far forward as you can to use whatever is left of the 2,800mm to streamline behind your head,like this Summers Brother's Goldenrod
*try to fully integrate your helmet as a bulbous leading edge to the fairing.
*integrating the roll bar into this rear fairing will help the flow to recover from the open canopy turbulence.
*if you can't get the roll bar inside the fairing,then streamline the tubing as best you can and blend it into the top of the shell to kill hook vortice formation.
*put your 500mm wheel track in the rear
*design the wider front track to agree with the streamline contour
*Fully enclosing the wheels,even though it adds frontal area,completely offsets the interference drag of 'open' wheels.