What is the best/biggest sissy bar bag or trunk bag for very long travels on a motorcycle - 5 week trip?

Need a bag with a lot of room.
Thanks for the feedback. Actually looking for my father and he may be going with a Full Dresser Bag from Bagtec, because he finds the rigid compartment appealing.

http://www.bagtec.com/FullDresserBag/

When loading a bike the rule of thumb is low and close to the center of gravity. However If your riding a 600 - 800 lb. bike it is not as critical as with a 300 - 400 lb. bike. Hence things like tank bags, tail bags and saddle bags are popular with riders on mid weight bikes. Larger bikes can use sissy bar bags with fewer ill effects.

This place has a very large tail bag. They make their own bags in their shop for each order. You can have them make custom bags also.

http://www.magsbags.com/grandtouringbag.html

Here is a sissy bar bag, but it is not as large as the Mags Bag. T-bags have been around a while and they are very popular.

http://motorcycle-luggage.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MLTBU304&Cat egory_Code=

Here is another very large bag, I can't vouch for it's quality, but it is big.

http://motorcycle-luggage.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MLK4140&Cate gory_Code=

A surplus Army Duffel bag !!! Hey it got me through the 60s

We don't have that problem.... My bride has a harley trike and we got a pop up camp trailer she pulls behind it... you may want to check on something like that...they hold everything you would need and then some......