The wheel arches are a good trap for moisture and dier which = Rust under them. I also think the rust starts from where the holes were driled into the sheet metal for the screws. once a hole is drilled, bare metal is exposed for rust to start.
I think the plastic bubble at the sun roof is more of a wind deflector when the roof is open.
Anniversary Addition?

Yikes!!! that is a very rare model, I think they only made one. grab it quick. surprised the guy isn`t asking $18,000 for it. Hurry before the price goes up
Charlie