They have a sectional stiffened back piece and long shoulder straps!
Can't see it being a problem for a larger gentleman, my friend is a larger framed person, i will get him to try it on tomorrow and let you know!
If you look inside the pack you will find two slots, one on each side at the back. These slots are ment for the issued poles for the tent sections we were issued. You could stick some alu tubes or something in these slots to stiffen the back up a bit.
Hope you post pics of the pack with side pockets, thats something I might consider doing my self.