King Kielbasa, I used Farm and Fleet, Tractor Supply, etc, black tractor paint on the underside of the wood floor on my 49 Suburban. But I did this while I was replacing the floor and it was out of the truck so I could lay it on sawhorses and paint it using a brush. I gave it 3 heavy coats. Its been 7 years and 5200 miles and still looks new. You might find it hard to do laying on your back under your panel. Good luck on your project.
Weeds
