Its rust, those are the first places to go along with the A panels and scuttle.
Edit: Although pretty much anywhere except the roof will try and rust. Id go for a solid car with mechanical niggles, over a rusty one that runs sweet. mechanicals can be fixed, rust...... your stuck with it until a spare few grand is around for a reshell/repair and spray.
Edited by MiniGrin, 02 July 2014 - 02:07 PM.