Junior looks much better after I painted the The Big Hole to prevent rust during my Portland trip. Instead of the correct 10 step process for long-lasting repair, I just scraped off the loose stuff, got off most of the rust spots, and painted over it with three coats of Rustoleum Gloss White Enamel. The color isn’t a perfect match, but it’s still pretty hard to see if you don’t know to look for it. I’m planning on doing some body work on this panel once I get back, so this is just a stop-gap. Sprinter are infamous for rust problems.
Details on my Sprinter-Source RV build page here.