Thanks Bomp!
Last night I started to replace the side windows with new glass and noticed the "U" channel was in really bad shape. I tried finding some steel channel at the local steel supply but everything they had was much larger than I could use. Luckily I had some window channel sitting in the corner from another project.
I ended up having to cut off some pieces to make it work but after a little grinding and welding I have some nice new window channels.
I'm not sure if these are galvanized or aluminised channels but they welded up nice and are a lot stronger than the originals.
It's hard to tell form the pictures but here they are.
You can see the old channel at the top and new one is below it. The old one had big rust holes and was barely holding together.
Here's the finished channel, I painted it but I didn't take pictures of it painted.
