GMG makes a very valid point.
Most modern and some not so modern ICE cars have moulded plastic tanks mounted outside the body and ahead of the rear axle.
I'm not sure how this could have been done using a trad chassis.
Assuming the risk comes from behind. But it you hit a deer carcass in Cornwall, a plastic tank ahead of the rear wheels is actually more vulnerable, and I can say from experience the fragments of deer bone will make a concerted attempt to penetrate the plastic tank. It happened to be a diesel, but realistically no place is completely safe from freak impacts.
