solotripper wrote on Jan 20^th, 2010 at 7:30pm:

I'm with M_M on this one. I use a Thermarest pad as a stiffener in my Granite Gear food pack. It's a 48" x 20" pad, which serves a camp seat and if needed, extra padding under my sleep pad.

M_M and ST -- I took your advice.  I found some half pieces of old yellow thermarest in my gear, cut them to size, (15 inches) and duct taped them together.  I think this is going to work.  The pads are lightweight, bendable, provide good padding, can be used for other things, and most important, they provide some stiffness to an otherwise completely limp knapsack.  

Thanks to everyone for all the good ideas.  

prouboy