Thank you, I'm in the South East so I've never dealt with this.
Can't speak to the cleaning part (I've always just used a pressure washer and some car soap); but I swear by fluid film. If you're in the South East and not coastal, corrosion inhibitors really shouldn't be necessary (unless it ices enough that your DOT uses salt). That said, I've researched the crap out of this after my 4Runner frame was orange in more places than it was black. I couldn't turn a nut/bolt under there without a day's soak in PB blaster. What I found is more "permanent" coatings are pretty much always a bad choice. They all fail eventually, and when they do end up being far worse for metal components than no coating.
My Tacoma was in VA with me for 4 years before I moved to OR. VA uses every kind of road salt (salt means any chloride) and it does a number on truck frames. Mine looks pretty much like new but for all the dirt. Every year around November, I'd jack up the truck, throw on a tyvek suit and use about 4 cans of fluid film (and a wand attachment like this:
https://www.amazon.com/Fluid-Film-S...words=fluid+film+nozzle&qid=1585954147&sr=8-4) to get in every crevice and in the frame rails as much as possible. Come March, I would power wash the underside of the truck and move on. It would cost me around 40 bucks in "stuff" once a year and held up great. For the cost it's one of the better choices you can make ($9 to $10 a can at lowes or Home Depot). Cosmoline (and there's one other that dries waxy that I can't seem to remember) are definitely solid products but at the end of the day, it's still disposable and you're still going to want to coat it annually and they run about twice as expensive.
OA