been there, done that! as people say, once its gone in one area, it usually points out that other areas will be near the end of theyre life. BUT there is a chance that the car was scraped underneath (or similar) and allowed water/salt/shit to get at the metal and rust it. ive seen 1998 plate mondeos need wleding on the sills, only because theyve been hit underneath and corroded. it doesnt allways mean the end of the world like some say.

just take a serious look at the rest of the car.

BOTTOM LINE IS THE CAR IS MADE OF STEEL AND WILL RUST. Just weld it up, make it safe, and continue having fun with it!