You can suss those things out, theoretically, through finite element analysis and modal analysis. But then practically, you discover the modal and elemental differences between your model and construction in flight testing.
Rutan is f'n in love with that configuration. That was the basic paradigm of the Rutan Voyager... which ground its wingtips off on takeoff. It's the basic paradigm of Rutan's White Knight. Both of those craft, on the other hand, have a fuselage in the middle. WhiteKnight Two, which first rolled off the assembly line ten years ago, has a whopping 300 hours of flight time... none of which have a load. This thing is basically the WhiteKnight Two, only ridonkulously large.
The Nazis did something similar with the He111 Z1. However, it towed its load. It didn't drop fully a third of its gross weight from one pivot right at the middle of its stress concentrator at the peak envelope of its performance.
I don't like the modal problems. But I really don't like that they're going to rear their heads for the first time at 70,000 feet.