| Ventura every time!
There are two parts - a frame and a rack. The frame bolts under the seat which then carries the rack. The rack is designed to take the specially fitting bag. The bag slides over the rack (the sticky-up bit which is like a back rest) and clips underneath, so it doesn't go anywhere and is easily put on and taken off.
When you get to your destination you can simply take the bag off and the rack too, leaving the hardly noticeable frame.
I've toured in France loads of times and wouldn't go without one now. They're not cheap (about 80 quid for the frame and rack and 100 for the bag) but it saves so much time and effort with bungy cords and scratchy tank bags. | 
antonye
Hybrid Mode
