Rust Rocker Panel

Hi all
Bought a 2005 Prius about 3 years ago that had some small cosmetic damage on the passenger side rocker panel in front of the rear wheel. Over the past couple winters the damage has rusted and I have always put it off as a "next year problem". Now it's the next year three times over so I think I need to address this. See images attached.

The rest of the car body is OK, and yes of course the undercarriage has rust after 15 years in New England. For example the muffler had been rusted out and I repaired that.

What is the best way I can DIY a repair to prevent or at least mitigate further damage? Car is at 220k miles and has other issues so I really am just trying to hold over another year or two until larger problems cause me to have to junk it.

Thanks!
-J

 

Thanks, I will give it a shot when it is a bit warmer and post some pics.