If you really want to increase your range & don't mind spending some $$, I have a drawing of the saddle tanks I had made for my D90 (UK, RHD). They replace the origional tank under the drivers seat & also one on the passanger side but I had to relocate my battery to do that.
Modifying the front mounting bracket is easy.... cut the welds, flatten it & rebend the opposite way, then weld it back up. I also used an electric tank change-over solenoid to handle the fuel supply, return & gauge sender wires. Works a treat & you can switch on the fly with no issues.
The tanks will fit inside a Southdown tank guard but I 'squared' it off & reduced the clearences to squeeze a couple of extra litres out of it. Southdown also made a custom guard for my passanger side to match the drivers at the time. The tanks were fab'd in alum as they would be protected by the guards. You could get them made in mild steel or St/St to suit your budget.
Will post a pic laters when I get home.