The Givi WP400 is a soft bag that you can sling on a back of pretty much any bike. The bag is 100% waterproof, with a roll-up top to keep the contents dry even in poor weather (I still put all my stuff in carrier bags inside the Givi bag just in case – it’s a habit of a lifetime). The bag attaches to the bike with a couple of bungee ropes and sits on the pillion seat, neatly out of your way. It’s easy to take off the bike and even comes with a detatchable shoulder strap.
To give the bag a proper test I took it on a 1,400-mile trip to Scotland. Here’s a short video about how it performed on the road: