I love this kind of "do it yourself" stuff. I have included a bunch of links I have come across for various ideas on home made panniers of different types. Might give everyone some good idea of what they might try.

I think yours rock.

DIY panniers

Rucksack panniers

DuctTapePanniers

homemade-bicycle-pannier-links

Backpack-panniers-that-are-still-backpacks

http://www.crazyguyonabike.com/doc/Buckets