Fluid FilmOne Gallon Corrosion Inhibitor Multi Purpose Penetrant and Lubricant

You can't screw it up. Spray it on & hope it doesn't rust at all or expand. Works great

This keeps my vehicles rust-free really well despite the copious amounts of road salt here in northern new england.You have to reapply every year or twice a year because it washes off.As far as I know this is also non-toxic.Other than washing off after a few months it smells bad for a few days after spraying on.Don't spray it on rubber parts because they'll swell.Best to apply when its still 50-60 outside so it flows well and easy to spray on.

Sprays on easily and economically. Non toxic and great rust preventative. I use it on all my cars/trucks.

Great stuff to help reduce rust

Good undercoating for nh vehicles. Lanolin sheep snot easy to work with . Get the spray gun kit with wands for tight spots. Or just use plastic or brake line extensions.

Great product

Been using this stuff for several years, it's great because it's clear it don't hide anything.

A lot of people spray this on, but I've had good luck with putting the can in a pot with lukewarm water and slowly warming it up. Then I pour some into a shallow tray or a disposable bowl and use a paint brush to apply it to the bottom of the vehicle, taking the time to thoroughly coat all exposed metal surfaces other than the muffler. The end result won't be as good as a professional undercoating job, but it's a lot better than nothing at a small fraction of the cost. You'll use a quart or maybe even less each time, and you will want to recoat the underside every 1-2 years or so. One can of this could last up to 8 years, maybe even longer.