Always did worry me about the strain on the wings with full main tanks with a bit of turbulence!!!
Why would this be of any concern at all?
The main tank placement actually relieves the loads placed on the spar joints at the centre of the aircraft, increasing the zero fuel loading ability and distributing the load more evenly across the span.
Several reported reasons (besides the one I just mentioned) as to why the mains were located here include stability about the londitudinal axis and in turns (from the C310G, the tips took on a more aerodynamic shape - "stabila-tips") and crash survival (the tips supposedly separate in the event of a ground impact - this occurred to the second prototype. The tips broke away from the wings and it didn't burn after impact.)
Never could think of a good reason for that fcuked up fuel system, though. Byproduct of adding the aux tanks after the first couple of models?