I would love to see an extended range auxiliary tank that mounted in place of a spare tire while allowing the spare tire to sit above it. That would be cool.
Because my car us driven a lot on the street, I wanted to carry a spare tire, so I mounted my 8-gallon fuel cell in such a way that I can still use the spare tire wheel well for a wheel and tire. Its not the prettiest thing in the world, but it works...
I use the original tank for pump gas and the fuel cell for hi-octane race gas.
Sorry for the duplicate pic..
I like to keep anything that explodes outside of the car. Fabricated and tig welded in this sump to the stock tank so I can run 3/8" fuel line to the front of the car.