As long as the tanks are maintained with fuel on the inside, the only corrosion will be to the outside. And as any Sailor will tell you, if it moves grease it, and if it doesn't move Paint it.
The point being, the brass parts can be coated with petroleum jelly to prevent corrosion as the brass connections are designed to slide against another connector IE move.
The body of the tank however will just need to be painted. The inside of the tank if kept with fuel will have no Oxygen to allow Oxides to form (Rust).
Propane does not break down, so there are concerns with adding anything.
Oh and a side note, if opening a valve on a propane tank and temp is below 40 degrees, OPEN THE VALVE VERY SLOWLY Else the safety feature will think that the valve has a rupture beyond it and will decrease flow to almost nothing.