Alsan

Well I'm not too technically knowledgable on bikes and equipment. But I recently got a new bike and while in the shop I asked them to put a rack on the back, and I chose what I believe is called the, Ortlieb back roller classic. I have no adventurous plans like yours (good for you) but I can say that the ortlieb bags are solid and reliable. They clip on and off magnificently easily and seem to provode a very large amount of storage space and come with shoulder straps to carry them with you if you need to. They're also totally waterproof.

I went shopping the other day and was amazed at how much I could put in the bags. And I must say it didn't make any noticeable difference to the feel of riding the bike. I would have forgotton they were on the bike if I hadn't kept looking around to see them, I just love the red colour with the white of my bike. I got ortlieb because I had read good reviews. And I'm always of the opinion that it's better to spent a small amount more on a higher quality item rather than try to save twenty or thirty pounds with cheaper options. You'll be happier with them, they'll last longer and ultimately in the long run it's probably better value.