ducktapeguy
Adventurer
You could also looking into a custom made aluminum fuel cell from a hot rod shop or marine shop. I seem to remember pricing those out a while ago and the cost was fairly cheap compared to a gas tank. Probably due to legality and certifications required to sell something as DOT approved vs. off road use only. Something like this is pretty common at hot rod shows
http://www.ebay.com/itm/New-Polishe...ash=item2389b3b47e:g:ReIAAOSwal5YED-p&vxp=mtr
http://www.ebay.com/itm/New-Polishe...ash=item2389b3b47e:g:ReIAAOSwal5YED-p&vxp=mtr