Repairing the rusted wheel arches - 2011 GMC Sierra

I was shopping for a used truck a couple of years ago. I wanted a Tundra but those are hard to come by. So I decided to look at this 2011 GMC Sierra 1500 It seemed to be a pretty nice, well-cared-for unit. 

I look for certain things when I'm evaluating a vehicle, like if the previous owner actually cared about the vehicle beyond just doing the maintenance. There are hints, like

• the parts used for maintenance are not cheap brands
• the owner touched up rock chips 
• there are no holes for aftermarket equipment
• aftermarket equipment is not cheap brands
• the engine compartment looks completely original
• the bed is not beat up
• the interior looks like it's been cared for
• the wiring has no taps or cuts

This truck had all those features. It did not seem to be abused. The mileage was right, the tire wear was right, and the oil pressure was right. So I sprung for it:

Nothing to complain about.

It came with trailer brakes and a hitch, running boards, wheel arches, and a tonneau cover. I didn't really like the wheel arches, because with stock rims and tires it made the truck look out of proportion. After a few months I decided that I would rather not have them, so I took them off.

That was a mistake. Here's what I found:

Uh-oh. Well, crap. And the other side was just as bad. It seems these trucks had a real weakness for rust around the rear wheels. Now that I found my rust I notice it on just about every truck of this vintage. 

But I can't just put the wheel arches back on. I'm not like that. We're going to repair it.

I started with the passenger side. I marked it out, leaving enough for waste, and made my rough cut:

So we see the outer skin wasn't the only problem. The flange on the wheelhouse was gone as well. So I cut a section from the replacement panel and started fitting it:

I spot welded it in:

It doesn't cover the entire damage, so I cut a couple of patches and stitch-welded everything in. I ground it smooth and gave it a couple of coats of undercoating:

Good as new. Now for the skin:

I laid the skin over the existing metal and double-cut through both panels. That left me with a perfectly shaped patch:

I touched a few spot welds on the panel, then started filling in the welds. Ground smooth:

Primered:

I spent several weekends blocking and primering to make sure I had flat surfaces. Silver doesn't show as bad as some other darker colors, but it still had to be right.

And now painted:

I wasn't happy with my clear coat job, so I'm probably going to respray. But it's better than the rust, and everything came out nice and flat.

Now for the driver's side. I found that I am missing pictures of certain steps. For this side we will have to jump to the stage where I've already made the outer cut and the inner panel is installed but not undercoated:

Here's the fitted skin:

The tape is to keep the replacement panel clocked properly.

Welded and ground:

Primered:

And painted:

This side came out better, but I think I can improve it. So at some point I'll sand down and respray.

These were difficult repairs. I would never advise a novice to attempt them.