Rust on outside edge of fender seam - Repair?

[Dispatch20]

I found some rust starting on the seam weld area on the rear fender. Normally, this area is covered by a rubber guard. I removed that rubber guard a year ago. It's not clear if removing the guard contributed to the rust, or whether the many years of having the rubber guard wore down the paint & galvanized metal. The car lives in the rust belt, so this isn't a huge surprise.

 

Any advice on the smartest way to handle this? The solution doesn't have to look that great as long as it delays the rust from eating the car away. The rust currently isn't perforated through any of the metal. However, it's on the inner seem edge so the surface isn't exactly smooth and easy to correct. Thanks!

[utc_pyro]

Sand, use rust converter, paint.

[Dispatch20]

Am I overthinking it? Basic primer and paint? Or some fancy rust cover like POR15 or rust bullet?

[fotofan]

That's such minimal rust, if you'd sand it down to bare metal where there's no rust left, then just hit it with a coat of primer and a couple of paint it would be just fine. Rust converter never hurts though.

[Dispatch20]

Rust converter relies on leaving rust on the surface so that it can bond/chemically change it. On a fender like this where I'd have good paint remaining adjacent to an area sanded down to bare metal, I'm not sure it would work. It might be better just to sand and prime. Unless there is a rust converter that would work different than most of the ones I found.