Extended range fuel tank

Hi all

I'm planning on a euro tour next year on my Monster S4Rs (with an exbox exhaust and power commander with custom map which hasnt helped the mpg) but the 80-90 mile range is not very practicle especially on the autobahns.

Has anyone commissioned a larger tank to be made and where they had it made, preferably in Scotland.

Another 5 litres would add a significant difference.

Thanks
Jim