I've never done it but it just occurred to me that my motorcycle chain wax might be good for this. Sprays on liquid so will penetrate, then drys to a waxy coating. Keeps rust off my chain anyway. Amsoil also make a metal protectant that I also use on my motorcycle.

 

this stuff: http://www.amsoil.com/storefront/amh.aspx

 

I just wiped down the bottom door jambs completely for the first time this year...... Still no rust. Not gloating, it's just that some of them have this and some don't. A bunch came through with incomplete gluing in the pinch weld, but not all of them. It's not a design failure, it's a manufacturing inconsistency.

 

my 09 is doing this on the bottom of the doors.

 

Depending on the climate and conditions the vehicle is in it will happen to them all at some point.

But like I stated it will be years before it reall get so bad that it can be seen on the outside of the door. At this point most will be well used high mileage HHR's.

The only sure things in life are taxes, death and rust.