Rustoleum on your undercarriage ??

I've got a cheaper and stronger answer for you

Tractor Supply "Truck & Trailer" paint :glasses7: Damn near bulletproof and it doesn't matter how you apply it, or to what surface it's going on.

Sprayed the dumpbed on my dad's D300 Dumptruck with the stuff about 6 years ago, all we did was take a wirebrush to some of the flaking paint and washed the dirt off with a hose. Waited for it to dry and then sprayed the Truck & Trailer Paint on over the rusty metal and remaining paint (no primer).

That paint is still intact except for a few locations where hauling junk wore it to bare metal. Didn't matter what we dropped in the bed, it didn't phase the paint.

Also sprayed the bumpers on my offroad truck (D50) with it, I've wrapped chains and winch cables around the bumpers, it hasn't even scuffed the surface of the bumpers.

Brushed it on the Snow Plow for my grandfather's plow truck 3 years ago (the plow still looks brand new). Brushed it on my plow earlier this year, and I've pushed piles of stone, firewood, etc with it and it hasn't even scratched the paint :D