Obviously you dont want it wet with sea water but salt is only a problem when air can get to the metal. De-watering products that leave a continuous oily layer will prevent corrosion even on surface rusted metal. Flaking rust or failing paint will leave open areas for corrosion to continue so must be fully removed before the area is treated. Rust converters are good, but they can't do much with thick rust or where paint has not been cleaned off. Rust creeps under the edges of paint. Oily surface treatments soak under rust particles and stop existing rust continuing. Top them up annually to catch flaking areas.
I was surprised at the effect of chainsaw bar oil thinned with white spirit. Solvent thinners would also work but risk overspray paint damage. I treated some rusty metal and left it out to weather. The oil had gelled like a varnish but remained soft. I cleaned off 1/2 of the area and left it another 6 months. The original surface was untouched. but the cleaned off area was still quite bright with minimal corrosion. It should have rusted up badly but really didn't. It shows how important it is to properly clean metal before priming and painting. It also showed how an oily layer keeps the elements off the raw metal.
There are examples on You Tube where people have used phosphoric acid followed by epoxy primers inside box sections. It's all very well but any rust in spot welded seams will not be deal with. The acid treatment followed by the likes of Lanoguard or even thinned chain saw oil are more likely to soak into the seams and stop the corrosion. Epoxy primers hide the carnage going on beneath. Waxoyl used to be the "go to", but it's too viscous to run into seams and it does dry out. Who wants to be doing that job every year?