On the seatstays you can use p-clamps from Ace Hardware that are wrapped in rubber. Your bike has short chainstays so to avoid heel-strike if you have big feet you'll need a rack that can hold bags aft of the rear axle like the Blackburn you linked to or like the Axiom racks with brackets on the bottom. Use thread-locking goop on all the bolts. It might also be a good idea to buy panniers that are angled like the seatstays, for example the vintage trapezoid-shaped Cannondale panniers.