I use fluid film in PA winters and it works very well. I spray the vehicle when new, getting inside panels, doors, tailgate, etc. I then do touch up annually in the Fall to prepare for winter. It does a very good job. You don't need to spray it on thick...just a light film. If it's dripping, it's too much (IMO). My truck has seen a couple winters and has no rust. In high wear areas (like near wheels where you pickup wash from the wheels, it will wear off), I buy a small can and do touch up a couple times per winter (pull the truck in the garage, warm it up, wash, and dry...then spray).
It's the most cost effective, easy to apply, and highest performance stuff I've used. Not saying other things aren't out there...but FluidFilm was developed for the navy. I use it on all my equipment with great results. I purchased a sprayer and buy the FF in 1 gallon containers. I like it.
Note, it will attract dust and dirt. So, if you want a spotless undercarriage, this is not the product for you. But, I powerwash annually. I am more concerned with keeping rust from starting.
I used the product on previous vehicles (last one was 2006 Tundra - that I traded in 2012 and it was immaculate underneath (no rust - on welds, panels, frame, etc).
