Body/paint floor questions

I have used Amerilock paints and its extremely durable. It has very high solids and covers great. The down fall of using it on a car is that its not flexible at all and will crack. Not to mention, its very expensive as far as I know. We use it at work (petroleum storage plant) on tanks and pipelines.
I used it on the inside and bottom of my car and then went over it on the bottom with spray in bedliner. Its very unlikely this car will ever rust again. But like I said, its very hard and will crack or chip if something hits it hard.
You want something cheap, get some rustoleum rusty metal primer. You can thin it and spray and its much like the primer mopar used back in the day.