Typically multiple layers as you are describing make a good moisture trap, for a short-lived repair. You would be better served to cut out the rusty metal and weld in some new patches. The straight sections would be bent up on a sheet metal brake. For the rounded corners, there are many ways of accomplishing those. Here is a thread that I added a how-to on forming these. (please excuse the web site....bare sheet metal doesn't care what brand it's fixing)
Fabricating windshield corners Or they can be fabricated using hammer forming. Here is a thread where I repaired a wagon tailgate using hammerforming, it may give you some ideas..
Tailgate repairs using hammerforming And finally, this last link is not my work, but be sure to also read metalworking II and III while you're there, some awesome work and a good demonstration of what can be accomplished to repair the rust.
Metalworking windshield frames 
