No rack, no problem. Banjo Brothers' Waterproof Saddle Trunk has the capacity that you need without installing a rack. It has a whopping 400 cubic inches of space with a waterproof main compartment and outer pockets for easy access to smaller items. A webbing loop on top lets you lash a jacket to the bag so you can reach it before the rain comes. An interior aluminum strut, stiff hull and 4-point strapping system control the load from bouncing, rattling or swaying. The best part is when you're done with your ride, you can remove it quickly and it works on pretty much any bike.
Capacity: 400 cubic inches