Ive been toyin with this idea for a while too....
I want a decent leather bag at a decent price that I can lay between seat and rear fender mount on my k8 without having special mounts and not rubbing tire. Heres the best Ive found for my bike. This bag is sold at a place called Atwoods, dont know if its a chain or not, for 40 bucks. Good price. I believe with this bag and k8s, you could lay it between seat and fender mount and over the grab rails, and it should lay mostly on the shock uppers so a bag frame wouldnt be needed. I guess you could seperate the leather at the center point if you wanted to keep them portable and still run them between the fender and under the grab rail, and reconnect them. Leather lacing and eyelets, snaps, zippers, duct tape, etc... With my situation I dont really care if they are that portable so Ill take off grab bar, put em on and put bar back on. A person could still take stuff out of the bag but they couldnt just walk past and take the whole bag off my bike.