Underbody Shield problems of the 2002 Chevrolet Cavalier

Engine cradle subframe has rusted through on right side. Low mileage, car is parked in a garage, so it does not sit outside all day and night. My mechanic tells me he has seen this a lot with chevys. He says it is especially true with gm cars driven in the north because of the weather. . . So much for being imported from detroit; isn't that in the north? he says he can order a used replacement from the southern us. I know a Cavalier is not a top-of-the-line car, but isn't the frame supposed to be the strogest part? come on gm, fix this issue before somebody dies! I was going to let my 16 year old kid drive the car, now I have to tell him that he can't because an affordable car made by the biggest us automaker is cheaply made and unsafe!?.