It happens more than some think. In the north, salt and snow cause rust under a vehical. Down here sun damage, humidity, moisture and lack of maintenance do it to the areas most exposed to the sun. Uv rays and heat will peel the clear coat right off a car without uv protecton.
The holes in the roof let water leak onto the floor causing the floor to rust. But other than the roof and floor, no rust.
98 XJ 4x2 to 4x4 converted