I'm getting ready to order the Touratech tank. One reason is the 65 mile commute I have (one way) and fuel cans don't solve the issue. The fact that the back of the bike is still open and usable leaves me enough room to carry my work related items on the back of the bike so that I'm still able to split lanes (thank's CA!).
9.5 gal of fuel should be sufficient for commuting 3 days (400 miles). Maybe if I'm lucky I can make it 4 days
(usually get about 56mpg commuting).
Sure the tank is expensive but there is one BIG advantage. It doesn't change the ability to pack up the bike like all other options people propose and implement.
I probably should have the whole thing worked out some time in Feb (or early March) and I'll be posting additional information once this is completed. I originally thought to do the install myself but most likely will let the shop do it (unless they charge another fortune for it).