Thanks for your help, guys. I'm not comfortable with the do-it-yourself backpack/pannier conversions due to my lack of skill in such things, concern for the backpack's construction, and comfort in wearing a backpack with such an improvised system, if it should work out. The bungee net method seems to be limited to lighter, smaller backpacks. Would a bungee net be good enough to secure a backpack filled with textbooks, binders, and smaller items? A rack-mounted container seems pretty safe, although it would take up the rack and need to be removed for other cargo options.