I did a week across the Alps in June, it was the best thing I've ever done in my life, you are going to love it!
I used an Oxford tail pack and a small 7 litre magnetic tank bag.
The tail pack was strapped around the passenger seat, and then bungeed to the rear footpegs and the other bungees pulled tight under the tail unit and hooked to each other.
Make sure you pad out protect any part of the bike that is touched by the luggage. A small bit of inclement weather and the tiny movements will have the luggage acting like sandpaper. My seat unit took a bit of a beating and needs some good products and elbow grease to restore it.
If your luggage is strapped down evenly you'll be suprised how little force it needs to stay on the bike. A lot less than you'd think!
