Help evaluating this car...69 DART

Can someone confirm by looking at pics of initial car I posted that it is normal to have a fiberglass looking substance sheeting the inside of the quarter panels? The craigslist ad has a trunk shot that shows this. I guess this keeps the qtr from wrinkling.

...am in process of negotiations right now. checking out the floorpan and going from there.

1969 DODGE DART