I have a 2010 and the rear half of the rear wheel well lips are rusted. The metal is still there so I just want to clean and repaint.

The bottom surface of the lip (facing towards the tire) will be easy to access but the upper surface will be difficult.

How best to remove the rust? What products to seal the metal? Where is the paint code listed and where do I get matching paint? The match is not that important since the location is hardly visible.

Most importantly, will this really help to slow it down? My success in stopping rust in seams of other cars has been zero.

 

The best way to handle rust is to prevent it. Once started it can be very difficult to stop, especially in the seams where dirt collects and water is slow to evaporate. "Sealing" the seams after the rust has started will not stop it and I'm not aware of any product that will stop rust in a seam.
Here in the North East, your vehicle must be treated with aftermarket undercoating products when new to even stand a chance at surviving a handful of years without rust making it's ugly presence known. Our '01 was treated by a local company and still looks good after 14 years, but it has rusted in places you would not expect...

 

^ thanks.
I just took a closer look at the lip and there is a seam and the gap is large. There is no way I know of to stop rust occurring in the seam.

 

You can try the liquid products that turn rust to a black color. I can't think of a name brand, but they will stop rust. They should be primed and painted after they have finished their chemical reaction. I believe they have copper that gets to grab the O2 but am not really sure. I have used one and had decent success. You may be able to push it into a seam enough to reach further than you can get with a brush. I use an 'acid' brush, narrow with a rolled metal handle to daub it onto the rusty surfaces and try to push it up gaps.
It will generally not hurt painted surfaces, and will remove using a rag and water, or wax/polish.
It may just slow things down, but it is better than nothing.
tom