Three cents from me:
NHOU, Krown Canada, Fluid Film (Germany) and the good old redneck lithium grease thinned out with Diesel slathered over the rocker panels that live beneath those usual plastic covers are the tricks up my sleeve that I've tried, if you mean bare metal or superficial rust without any primer coating. Because Poland uses salt for winter maintenance. ("Stop blowing holes in my ship!") (Luckily, with the ban on cheap road salt from Belarus and Russia, there won't be any White Death on the roads this year, LOL!)
I used to own a '00 Grandma Keith
which had the typical Panther platform rust issues (thanks, Ford, you're retarded). Superficial rust on the frame, one seam below the driver's seat was getting ripe, the trunk floor drains were goners. I had it oil filmed at my local Krown shop (they actually ran the underside ELEVEN times until superficial rust said it wasn't thirsty any more, LMAO!), I broke out Fluid Film Black (the gooey, tar-like version of their mineral oil undercoat), warmed it up to make it flow and went wild with a big ass painter's brush around all seams, round the chomped out trunk drains, and whatever looked suspicious or worth enough the effort. Didn't bother with the frame section internals (Krown did that for me); removed all water from the door panels with a ton of WD-40, left it to drain for several days, used some off-the-shelf 'cavity wax' spray that came with a handy wand.
In short, this treatment stopped the Red Cancer (tee hee) and I didn't see it progressing until spring (TBH, I work from home, but the car saw some operation on salted roads...).
Removing rust is essential. Superficial rust doesn't necessary need removal, save for the loose debris, dust, all that stuff which peels off. I know people who represerved that with marine-grade 'brick red' paint and reported success, but only with some sort of topcoating or oil coating. Conversion coatings work well, too, but they can't reasonably be left alone without something over them.
I second washing the car regularly to remove all the chemistry which triggers or accelerates rust, followed by represervation - at least with some anti-rust oil.