Hey Korruptor,
I have the soft saddle bags. They work pretty well and are pretty well water proof. They don't seem very big, but you can jam a good bit of stuff in them. They attach with nylon straps that go under the seat, one goes around the license plate and two go around the passanger pegs.
I didn't want to buy a hi dollar trunk, so I took a Ryobi 14volt drill case and attached it to the back half of the seat. Works REALLY well, and didn't cost anything. I can send some pics to your email if your interested.