Scotty,
I live in the salt belt, and my 2010 GMC Yukon has the classic rust starting on the cab corners.
I tried to do a patch myself before the winter. I sanded off the rust, used some bondo, and then painted matching rustoleum paint. But the rust is back.
Without having to pay a bunch of money, how can I neutralise this rust from growing? I don’t need it to look perfect, but I for sure want to at least stop the rust from getting worse.
The only way to stop rust is to get rid of whatever panel is rusting before it spreads further. There are no effective bandaid fixes and repairs will not come cheap.
I lived in the snow belt for 56 years and in my opinion, anything you do will be a stopgap measure. The rust is moving under the paint and if you took the entire fender off you will see what I mean. A whole fender replacement may be necessary but if one is going, the others are sure to follow. That's why I drove beaters for work cars and got a different one every 2 years or so. That's not, I'm sure what you wanted to hear but salted roads are murder. Try the Rustoleum Rust Reformer, I've used it on other things and it works pretty well.
It probably won't do much, but you might try an aerosol or brush-on rust converter with phosphoric acid. I think Rustoleum makes it. It converts surface rust to black iron phosphate, which is impermeable to water and doesn't flake off. Get off the loose rust and dirt, spray it on, and it should help. If you get chips in the coating, it will rust again, and any chips in the metal beyond the phosphate layer will rust it off..
Cab corners are notorious for collecting water and rusting from the inside.
If you can see the rust from the outside it's already too late.
