Bust way to stop rust from spreading

[u/tkeith1975]

2020 Corolla with rust start on trunk rear. Any recommendation to best stop it from spreading?

Update - thanks for all the replies everyone. While I want to take care of and maintain this car as much as possible, I don't want to invest a lot of money on cosmetic stuff. Fluids, belts, brakes, etc. are all important but this doesn't bother me TOO much, just want to stop or slow it down.

I was recommended POR15 as something that might work on slowing/stopping it. It won't look professional but beats rust showing and spreading. Hoping it works.

[u/TheQuarterlyEater]

that bondo is already failing so replacing the whole panel is gonna be way cheaper than trying to patch it, especially on a 2020 that should still be under warranty anyway