I don't know how well any of this attaches to racks (although i did see a thread earlier about using PVC to mount backpacks to a frame) or how well it holds stuff. However, I will offer you an alternative storage system: See this post -
http://www.bikeforums.net/showpost.p...2&postcount=17. I got the idea from another thread a number of years back. Basically, I just stapped on a milk crate with some zip ties (I'm actually planning on putting some cheap side bags that I have on my walmart bike to increase my carrying capacity). When I was riding to and from highschool with my bike, my textbooks fit very nicely in that crate. You may want to give it a try.
The thing with mounting anything big on your rack like this is that you've just got to be able to swing your leg nice and high. That is where a step through frame is really nice.
Good Luck.