Thats a new one on me too. I know also the Brits tried a canvas bag on the wing of a Spitfire to carry personnel when moving locations but that didnt get past the testing stages really.
Looking at it again, can you imagine how effing loud that would have been in a thin skinned aluminum tube being about a couple feet away from such a huge prop!!!!!!!!!!!!!!!!!! JESUS! Another case where an engineer meant well.
I could imagine it wouldn't be the most comfortable ride either. I would assume the thing had to have some ventilation, so it would be stifling hot in the Pacific summer or nut-numbing cold in the winter.
As big as those look you might be able to fit portable oxygen tanks. The big problem would be the cold at high altitude. No place to plug in a heated flight suit's.