Where in the world do you live that you can't find a gas station every 100 miles or so? Nunavut?
But your plan may not be as simple as you think.
1) The pickup for the aux tank will have to be at the bottom, and that will put it at about axle height. Are you sure your fuel pump has enough pep to pump uphill that far? -- remember that your existing setup has the gas above the pump. Might be a good idea to test this first with a line into a gas can on the floor.
2) When the main tank runs low or dry you will need to have a valve to switch to the aux tank or the pump will want to suck air from the empty tank rather than gas from the aux tank.
3) That's a lot of weight on one side of the bike -- you might have to carry some ballast in the can on the other side.
Seems like a lot of trouble unless you really NEED it. I did have a bike that gave me range problems (a Suzuki GV1200 "muscle cruiser" that was good for only 100 miles or less when all four Mikunis were sucking hard) but on the very few occasions when I thought I might exceed that I just carried some extra gas in plastic soda bottles in the saddlebags.