Lots of cars had this same design in the 70s, with the fuel tank low in the rear, right behind the rear differential.
Jeep Grand Cherokees were this way between 1993 and 2004 and Jeep Libertys were this way between 2002 and 2007.
I do believe they were plastic though.
But they are jeeps. Quality was never an expectation
Always has been. This place sucks.