something like this, but bolt it to where the gas tank bolted to the trunk frame unibody to keep it structuraly sound. http://www.fast351.com/fuelcellbox/
[addsig]
avoid chinese tanks they come pre rusted...no coatings like the ones from USA or canada. try www.automotivepartsnetwork.com look up your aplication and if its not a fastback they have one for $171.13 + 16.37 shipping
I am looking for a '65 tank but might have to modify my trunk floor to install a later model "drop-in" tank instead...they stopped making the '62-65 tanks that are worth a damn