Did these cars come from the factory or dealers with some kind of undercoating?

I used five or six, no more than six. It was about 5 bucks a can at Walmart.

Let me also add this. Make sure to use the "straw," that comes with it. If you don't, it comes out way too fast and wastes it. I used one without the straw, and I used it up 3 times as fast