Backpack becomes a pannier with homebrew frame.
I found a backpack at the local thrift store for $2 and decided I simply had to mount it on my touring bike pannier style. I looked at the combo backpack/pannier at nashbar and figured I could make my own. The objective was to keep costs low, as I did not want to spend more money than what the nashbar setup would cost to purchase. The material used for the frame is common and cheap PVC plumbing pipe. I purchased a 10' length of 1/2" pipe for $1.55. The schedule 40 pipe cost slightly more but I wanted the thin wall pipe for two reasons other than the cost. A reduction in weight and the ability to use the frame to carry extra water and thin wall pipe would hold a little more water. I also purchased two 90-degree elbows (15 cents ea)and four Tees'(17 cents ea). I made the frame long enough the shoulder straps would tighten up on the frame and made the width the same as the backpack. I used another pipe across the middle of the frame to provide a place to attach the frame to my rack and use some straps provided on the backpack to compress the contents and now they also help hold the backpack to the frame and keep it from sagging. No modification is done to the backpack so if required you can remove the frame from the backpack and use it as originally intended. If you're way out in the middle of nowhere and your bike is damaged to the point that you must abandon it at least you have a way to carry some of your stuff with you. I only used two 90-degree elbows for a reason. Two Tees' are used at the other corners to provide a way to fill the pipe with water and drain it for use later. Use caps, plugs, or valves on the Tees' as per your preference for filling or draining the frame. My frame will almost fill a standard water bottle. In retrospect I could have use 3/4" or 1" pipe for hauling more water. Mounting the frame to the rack was easy. I used Velcro straps made for bundling wire. A pack of them were found in the automotive section in a local Wal-Mart. There 12" long with hooks on one side and loops on the other and a slot is provided to run the strap through the slot around the frame and rack providing exceptional holding power. They're also easy on and easy off. Two are strapped to the top of the rack and the middle pipe in the frame and a third to the bottom pipe of the frame and a rack support. Below is a picture of the backpack mounted to the frame and my rear rack.