Worst car for rust I've ever owned was a 1976 Cortina 2000e & it filled with water every time it rained.
The front wings went rusty early on my MK3 Cortina but I don't recall mine actually leaking. Then again it had no wheel arch liners so the mud and crap accumulated in the top corner of the front wings. I had to replace the wings on mine. My SD1 was just as bad for rust, but it was the door bottoms and rear wheel arch that suffered on those, as the SD1 doors didn't drain properly.
Both of these cars were second hand though, so I sort of expected it. My dads Japanese cars were brand new, and he didn't expect such rot within a couple of years. The philosophy was, buy Japanese, keep it for four or five years as it will be reliable and then throw it away before it disintegrated and start again. By contrast, I had my 3.0S Capri, purchased at around two years old, for about six years and it had no visible rust on it.
The guy that bought it off me kept it as a collectors car, I just wish I had.