Try a simple change to the standard approach and that is to make a large, (Widest possible from a single sheet of foamboard), span single section for the centre, (over the fuselage), and fit either a spruce or CF spar reinforcement. the polyhedral sections begin from the ends of the flat centre section. By shifting the "wing Joints" outboard reduces the forces acting upon them and makes the wing far more resistant to folding or breaking under high stress loads.
The first polyhedral wing joints should be relatively shallow if the wing segment to be joined is long and the final "Tip wing piece can have a slightly greater angle and much shorter span. Effectively just the wing tip shape. With the wing tips think of changing the planform cut line to introduce washout into the design to give gentler stall characteristics.
Dihedral braces would still be recommended on the 2 inner wing joints or some form of wing detachment mechanism as used in the backpack spitfire. The wing tips could remain permanently connected to the wing outer sections, effectively making the wing a 3 section wing.
Rather than large ailerons with a huge powerful servo you can use trailing edge control surfaces on the 3 inner wing sections with 4 separate servos and the 2 control surfaces on the wing centre section being configured as "Flaperons" and the outer control surfaces as plain ailerons with the possibly of adding crowfoot mixing as well.
Additional measures to improve the rigidity of the structure could be considered. Firstly some wing or fuselage location blocks are recommended to stop the fuselage trying to slide along the wing during maneuvering with heavy loads. Secondly a set of wing struts could be considered fro the fuselage sides out to the centre section wing joints and finally wing leading and trailing edge surface reinforcement to reduce or stop the damage to the wing caused by the increased forces causing the wing hold down rubber bands from cutting through the wing.
If you require any further explanation of my suggested solutions please advise and I will explain further or someone else would.