Well done!
Yes, a single layer, composite lay-up would be a quick way to build your second fuselage. The thicker it is, the less it will bend sideways.
May I suggest planning it with bolted structural joints in both the top and bottom longerons?
In almost-finished configuration, the bottom longeron could be hinged under the propeller. For added stiffness, it could overlap into a trough/trench/groove that reaches almost to the the main landing gear.
The top longeron needs to be built in 3 pieces. The first piece is the forward piece (permanently attached to wing and cockpit) that carries flight loads.
The second piece of the top longeron is the aft part which is glued/epoxied to the single sheet aft fuselage. It bolts on just aft of the propeller.
The third piece is a cylinder/tube that rotates around the structural top longeron. The cylindrical tube only carries power from the engine to the propeller. Hopefully you can install a bearing close to the prop ... even if it requires a pair of diagonal bracing struts.
To replace the propeller )or drive belt) you un-bolt the top longeron and hinge down the aft fuselage.
Oh!
And to reduce noise, leave one bay of the aft fuselage uncovered until at least half the diameter of the propeller. You can still have thick longerons, just no covered vertical surfaces until you get as far aft as the fin.
Another poster suggested an electric motor with a huge hollow (10 inches?) through the drive shaft. But I suspect that requires an entirely new design of engine.
Meanwhile you are doing great with your first prototype. You will need many more evening hops to test its entire flight envelope. Enjoy those evening flights.