Never herd of plasti dip, But the implement paint will tell you on the can how much to use, and what hardener you will need for the temp you will be spraying.
I have seen a truck painted with a brush before and it was unreal how decant it turned out, it took a long time (a few hours to dry and laid down quit nice) ..... But I would maybe look at the single stage, price it and see, the tractor paint covers well, may as well go with a gallon, you will use it on other things maybe.
