School Of Hardest Knocks Dept...
RUST CONVERTERS, liquids you slop on and they turn black, work great BUT, and yet another BUT...
Fenders and brackets have to come off, breaking bolts in the process or no.
The rust converter has to coat EVERYTHING like a bio hazard suit.
This can be a problem accessing areas beneath crossmembers and forward near the hitch.
What happens in incomplete "conversion" (rusty holidays)is that untouched rust happily digs it way UNDER treated areas and keeps on eating. The converted rust and new paint falls off in patches.