It seems that sewing is in my future as well. The 4 oz. tent bag that has served as a backpack needs repair. In place of dedicated pads on the shoulder straps, spare socks are used. A string serves as a chest strap. In place of a waist belt, webbing is placed around the lower half of the pack and around my stomach. A garbage disposal bag keeps everything in the pack dry.
If you can measure, saw & nail a 2x4, you can measure, cut material & sew a rectangle. Tarps, quilts & backpacks (the bags) are all rectangles - bags are just rectangles sewed edge-to-edge to form barrels.
It's amazing how light a backpack can be. Even cheap rip-stop can easily handle 20lbs. And once you're UL, going over 20lbs is rare. If you're baseweight is 10lbs (or less), that would require 10lbs of food just to get to 20lbs.
As for pads, rather than socks, I would suggest spending a buck or so on 1/4" or 3/8" neoprene. Most hardware stores sell it as 2" squares cut from sheets, so they can cut you two strips to your measure.
Turkey cooking bags cost a few bucks, but have much higher tear strength than garbage bags.
Buckles are around 50 cents. Put one on your sternum strap, shoulder pads & hip belt to get proper adjustment. Here I am all ready to go @ SBL (I had come down from Langley the night before) from a few years ago:
Those are 20oz Gatorade bottles on the front straps. They allow dip n' drink on the trail, and put a little weight in the front as counter-balance. (They are perfectly level, they just look cockeyed due to the terrain I'm standing on.)
Here's rear of the pack @ Portal two days later.
Those shoes are New Balance MT110:http://wakesiah.blogspot.com/2014/03/new-balance-mt110v2-preview-july-2014.html
I'm now running/hiking in NB MT1010:http://trailrunnernation.com/2013/12/new-balance-mt1010-v2/
I'm getting a pair of these - perhaps for trails:http://www.lunasandals.com/
And also considering these for off-trail and rockier sections: