I looked at the BMW HP2 tank bag but it was outrageously overpriced so I picked up the Wunderlich HP2 bag from BMW Santa Cruz. It fits perfect, it's a snap to put on/take off. It's a 3 second job to unhook the front and tip it rearward for fuelling. It's 100% waterproof without needing a rain cover and it was less then half the price that BMW wanted for their bag here in Canada. I am completely satisfied with the purchase.
I have pics but don't know how to get 'em posted here. If you have an email addy I can send a couple shots showing the tank bag as well as the Wunderlich/Hepco&Becker Gobo hard bag system I installed.
Bario