I use Kreiga kit.
Take a look at:
http://www.kriega.com/categories/bike-packs/
You can mix and match what you need to whatever capacity you require and fit that either on the tank (with a protective rubber open mesh mat just like that provided for tool drawers), on the passenger seat and use a combination of US5, US 10 and US20 bag sizes.
I use a tank strap which allows the fitment of a US5 or a US10 bag. Over the rear seat its easy to attach a US20 and 2x US10 bags. They are not cheap, however they are waterproof. I have never had one leak yet.
Don't be put off by the pictures of motocrossers and modern day sports bikes. The straps are genius and they attach pretty much to any bike.
If you bought it and then decided to sell, they also sell for what almost what you paid on Ebay. No substitute for quality.
Only downside for some is that they are not hard luggage, however, again they are very robust indeed.