Y'all have given great Q and A here. Just the stuff I'm looking for. I'm considering a Chrome bag and have not yet decided on the size. My concern is waterproofness. However, I also commute in the winter (I use studded tires then) and wonder if there is a safety/control advantage to using a removable saddlebag(s) on the rear as compared to using a messenger bag. Any thoughts? I used to just strap things down on my uuuuugly Blackburn rack but now I need to haul files, books and laptop.