I don't know the Fuel capacity, RCJI says 4.1 liters in their articule....
it could be a mis-print 3.1L could be really what they meant.

The "takeoff CG" could be moved back with the addition of two tanks under the
engine mount bays giving you more fuel and a smaller total cg shift while in flight.
They would counter balance the main tanks for takeoff and first portion of the flight.

The best gear down "Dry" landing Cg concensus is the 110mm mark,
but the "wet" Cg moves forward alot after refueling. the tanks could balance some of this.

I plan on doing this to mine to keep the Cg centered with less shift.

I'm working on that gear door issue myself, the gear sit up too high to get it flush,
I'm trying to go to sheet aluminum, with blisters over the heads of the retract mounting screws.