L400 Gen1 or Gen2

[nxski]

You could always get the roof LineX'd to stop any rust!

I think that just hides it. They typically rust from the inside-out - mind did. The other problem with any type of coating on the roof is that while it conceals the rust, it's a red flag for resale.

It does rust from the inside out. If you take off the interior trim and spray with rust proof primer and paint after scraping off all the rust and applying bondo, you should be good to go. The general consensus is that moisture gets caught up there because of the heat from the lights, but it could be for any number of reasons.