Keeping the underside clean makes a huge difference.
Ever since I started driving we Baja'ed our trucks in saltwater marshes and the like, we always ended the day with a
thorough washing to prevent rust.
Now days, living gulf front we deal with occasional saltwater floods, parking high works if you know it's coming but heading out when there is just a few inches of saltwater on the road is common.
Clean them or lose them to rust.
What we've always done that is easy and works well has been to put a oscillating lawn sprinkler under our rigs and just let it run moving it and changing direction from time to time.
A couple hours of sprinkler time seems to be pretty effective.
I'd imagine with frozen winter conditions when these de-icing chemicals are being applied to your roads taking advantage of the first warm day would be wise.
Keeping accumulation points clear of mud, dirt, debris can take a little hand work but other than that it's pretty easy and very effective.
As always an ounce of prevention is worth a pound of cure.