Just got my 79 LeBaron back from the shop. As I plan do use it daily, I felt it's about time to get it properly protected for daily use - rain, snow, salt. All that usual and bad stuff. Mine had some minor protection on a couple spots, but corrosion inside started already. Thankfully no major corrosion, yet. Just about right to do it right. Some impressions. I'm not sure, if you have Dinitrol ML and 1000 (all cavities, insides) and ML + 4942 for the undercarriage. I'm very happy.
I used spray cans of this stuff on the under carriage of my, 89 Fifth Ave. even after bare minimum prep, it’s held up and worked very well Over the last two years of daily driving and Chicago, salty winter roads.
Yep, we get cars oil sprayed here to prevent or slow rust. The thick stuff that dries hard is good when cars are new but long term can do more harm then good.
Rubberized undercoating holds water out as well as it does holding it in. You get the added bonus of it turning into a greasy mess the moments it encounters oil. Used to be the only thing available here in Michigan, but they laxed the rules and oil spray is now available. It's really the only way to preserve vehicles in winter climates that use salt, but it isn't available everywhere.