Back in the early sixties my cousin did something I have never seen anyone else do for trailer axles and springs. Now lets suppose you have an almost new axle and springs. My cousin then grabbed some good marine grade grease and a brush...then applied the grease ( a bit of a thick layer) all over the axle/s and "packed" the springs as much as possible and all over bolts and such. After that, he got some burlap bags and covered/wrapped the axles and springs with two or three layers. He then got some copper wire and wrapped the burlap to the axle/s and springs. Usually the grease will penetrate thru the burlap so as to cover the cloth entirely. I know dust and dirt may accumulate on all this but it was better than your investment rusting up. Especially here in saltwater.

Another old school trick from down on the coast was to use linseed oil. Puts a pretty good semi firm coating on metal surface when cured. You could actually pull into a gas station and they would put your car on the lift and "undercoat" the car.