Last night, after a Harbor Freight run (finally broke down and picked up a welding table) I got the first coat of the rust converter paint on the mower deck
It needs to set up for a few hours - so I'll hit it with another coat tonight. Buddy of mine turned me onto this stuff. It's no magic bullet for rust - because we all know there is no magic bullet. It's mechanical removal (grinding / sanding / cutting out rotted metal) then treating metal, and that's still no guarantee.
That being said - he's been using this stuff on mower decks, truck frames, tractors etc - stuff that sees moisture and weather. As he's restored more than a few high $$$ cars - when he says something works, I take him at his word. Basically he said if you aren't stripping to clean metal, etching, epoxy / top coat etc - this stuff works well to if not stop more rust at least slow it a lot. He put it on a pitted up / rusted finish mower he was trying to just get a another season or two out - that was more than a few years ago.
He and I have both used POR15 in the past. Rust Bullet, KBS and others. All of them work well in their own way - but prep is the key. This stuff? It's cheap via Amazon. It goes a LONG way. Knock the scale off, clean it up, put a thin coat on, let it set up (works faster when it's humid) then hit it with another coat. UV doesn't seem to bother it much either, unlike some other coatings that prescribe a top coat for that very reason.
Tip - the paint has A LOT of solids in it. It comes in a plastic liner inside the can. Mix it up GOOD. When you're not using it, get as much air out of the liner as you can, then use a zip tie to keep it closed off. Personally I reverse the zip tie - keeps it tight, but you can keep reusing the zip tie. If not, pour in a mason jar. Don't get any on the jar threads though LOL. Cleans up fairly easy (hands / brush etc) unlike POR and some other stuff. As always YMMV.
Hope to get the SS in the shop tonight / early tomorrow morning and get the diff / ATF fluid changed out, get the deck / new blades back on the mower and then start working on the Silverado frame and melting some metal.