get an api tank, much safer.
you will loose bootspace though.
i have seen some dodgy donut tank installs as there is no real place to bolt them up.

All Fords have a big a** boot any way... go the API tank. My 5.0L has passed 250,000 kms on gas and is still as tight as a drum.

you loose boot space anyway with the donut's unless you're replacing the fuel tank for straight gas gotta keep your spare someware. or you could alway's not carry a spare tyre. car's don't need 5wheels anyway hell ive seen cars with 3 wheels and they worked fine.