Wobblybox
Hope this helps, I broke mine on a trip to Romania, it also broke the silver sub frame so there has been some work involved. the Givi mount is the standard ali mount (the horrid plastic one gave up) under that is an ali plate 12 x 14 inches X 5mm. As you can see there is a bracing bar going forward and down to the pannier cross brace (civils panniers and excelent bits of kit they are too)
I weigh close to 18 stone and I have sat on the the new mounting with no ill effects to the bike or me, it may not be pretty but like most of my stuff it works.
sorry the pics are so big (about 1.3 megs each, but if they have got there im as chuffed as a fart cos its my first time.)
Take care
Ride safe
John.