Depending on how much rust, and what your expectiations of the finished product is, you may want to remove the whole thing.

Simply drill out the spot welds "unbolting" it. Click on the link for the "Basics of Basics" of doing this. http://www.hotrodders.com/forum/basics-basics-spot-welds-removing-welded-panels-222549.html

Click on the link to see a photo of one removed.
http://i200.photobucket.com/albums/aa167/BasicsofBasics/My%20Truck/IMGP4326_zpsdbb2a452.jpg

Then you just plug weld it back in when done after the whole inside is protected with Epoxy primer.

Brian

Last edited by MARTINSR; 08/18/2015 3:36 AM.
1948 Chevy Pickup
Chopped and sectioned
owned since 1974 when I was 15.