These rack panniers in my opinion are just unbeatable, they are extremely cheap, extremely durable, light, reliable, compact and even completely waterproof. I've been using them the last months with complete success
You 're only going to need these:
2 x Backpack
4 x Hoseclamp or Rubber P-clamp
1 x Bamboo stick (around 1m long and thick like a marker) or a wooden broom stick or a branch from a tree etc
1 x Plastic sheet (2x2m - it's the one they use to cover things from the rain, you can find it in almost every hardware store)
1 x Old Belt
1 x Inner tube (if it's from a road bike don't fold it - you will understand when you get in that step)
4 x zip tie
2 x Bungee cord (depends - you can get them very cheap in ebay)
2 x Small steel carabiner or metal S hook
And if you really want to make it look cool:
Laminating machine (all photo copy shops can do it for you) or wrap it with transparent tape
I’ve made some drawings to help you get what I’m talking about. Don’t worry about the lengthy text is very very simple and very straightforward.
Ok, here is the main idea. You only need the naylon straps that are located on the bottom part of the backpack and connect to the shoulder harnesses (If your backpacks will be used only as rack panniers you can cut off the shoulder harnesses).
Now, take the strap and make a loophole with a knot so it won't get loose. Then take the rest of the strap length and make an other loop in the same way. If you do it right it will look like this (I). Do the same for both straps on the two backpacks.
Measure the length of the back of the backpack and add 10-20 cm (*). Cut two bamboo sticks with this length. Take the bamboo stick and make it go through the two loop holes. Do the same for the other backpack. Now take 4 pieces of inner tube (depends on the size of the loophole- but it should be around 10 cm each), fold them in half and wrap them tightly around the end of each stick. Then strap them tightly with zip ties (II).
We are almost ready. Take the carabiner/metal s hook and hook the right backpack (from the top handle) to the left part of the rear rack. Do the same with the other backpack but make it go through the top handle of backpack you already installed. (III)
With a piece of rope secure the hooks. I have permanently strapped a bigger piece of inner tube on each side of the rack (same thing you've done with bamboo sticks) so the metal hook won't chip the paint of the rack or slip left and right.
Notice the bamboo sticks prevents the backpacks from intervening with the wheels. Now, depends on your liking (feet size, backpack size etc) strap the bamboo sticks with the rack using the clamps (before you do that simulate the weight of the loaded backpack by pulling it downwards and strap it there).
You can hold all your things together by bungee hook the free loophole of one backpacks with the opposite one or with the rack. The possibilities are so many. You can take anything with you this way! I recommend You to cut two pieces of belt, open holes and tuck it on the stick between the two loopholes. Do the same on the other back pack Then bungee hook them with the rack to make them more compact and more secure (IV). You can cut many pieces of belt if you want more places to hook.
You can now make a sign with reflective tape or make a logo, a flag or whatever, heat seal it with plastic and hang it with rope from the ends of the bamboo sticks. It looks so cool! (V)
You can even make a wooden shelf on the ends of the bamboo sticks (you can make them big if you want to put more stuff) and put there a sleeping bag, clothes etc.
I used these panniers for the tour around Peloponnese. They performed just perfectly.
If it rains just stack the plastic sheet around your stuff and under the bungees to cover anything, it works even in the heaviest rain!
Now if you want to take out the backpacks just open the carabiners and unscrew the hose clamps with a coin and they are free!
Check my blog at: bicycleobsession.wordpress.com