Ronnie, I think if you weigh a standard Ford fuel tank vs a small alloy cell you'll appreciate the difference. Moving an alloy tank into the boot vs leaving a standard tank in place - I think you'll be saving weight and you're moving the weight of the fuel inboard - more towards the front of the car.

Safety wise, a rear end shunt is much less likely to cause a ruptured tank when it's inboard and in the boot.

Alloy tanks are typically foam filled.

Also all the pumps and swirl pots and lines are in the car so easier to work on and no chance of damage from curbs or underbody knocks.

Yes, it's a challenge in that you need to add a firewall, but worth it.

Charlie