I apologize if I'm not doing a good job of painting the picture here.
It's got both kinds of bags.
You're correct, the Kelderman mentioned in my sig isn't a capacity-increasing thing. Its only function is to smooth the ride mainly when empty. Makes my wife not hate the thing.
It's also got over-the-axle bags to stiffen it when it's loaded. I''m just thinking that using a tandem pair of over-the-axle bags would be easier on the frame, the bag mounts and the bolts that attach them.
Seems to me that spreading the load over twice the mounts at lower pressure can't be a bad idea.
It's not that the current setup isn't working... its partly that I'd like to spread and reduce the stresses and partly that it ain't broke so I feel the need to fix it!