Multivario tankbag, with 3-pocket fanny pack addition holding a 64oz. CamelBak
Given that I own Eclipse, OSI, and Bagman tankbags, I nevertheless chose to buy and use the (very expensive) BMW Multivario tankbag. I made this choice for two reasons; stability when loaded and utility while under the rain cover. The Multivario attaches to a base which is very firmly snugged onto the tank it will tolerate VERY heavy loads without shifting around. As well, the Multivario is the only tank bag Ive found which has a clear top to its rain cover, allowing the maps To be read even when the rain cover is installed. (If youve never done A lot of traveling cross-country in the rain, you wont appreciate What a big deal this is, but trust me it is.)
To augment the Multivarios capacity, I strapped a 3-pouch fanny pack around the Multivario, with the pouches facing the riders seat. This allows me to store my CamelBak in a location which is accessible and which allows the CamelBak to produce condensate in the summer without fear of soaking important travel items (as happens when placing the CamelBak in the tank bag itself). I chose the 64oz/ CamelBak because It is designed to be mounted "landscape", i.e. with the long dimension Horizontally. It is a bit larger than the fanny pack pouch itself, but Can be fitted into the fanny pack when slightly less than completely filled.