I have the Kuryakyn Ultra Tour bag. It's a great bag, but a little heavy and not waterproof. It does come with a rain cover, but when you're riding in and out of the rain, it's a little inconvenient to take the cover on and off to get to my rain gear which I store in the bag.
I'd love to get a slightly smaller (and hopefully, less affected by cross-winds), waterproof bag that attaches in a similar way as the Ultra Tour bag which is with a large velcro strap around the passenger backrest. It literally takes me less than 30 seconds to put it on or take it off and that's with 4 additional security straps.
Of course, I could get a trunk (like the Givi), but they're not compatible with a passenger backrest unless it's extended further back than I would like. Yes, I know the top boxes come with built-in passenger backrests, but I've got the bike set up just how my GF likes it and I'd like to easily add or remove a trunk bag depending on the length of the ride and weather.
Anyone know of such a bag?