I rolled on Rustoleum 8 years ago. Full strength and right out of the can. I did not do any prep work. Just layed the paint over what was there. I just wanted the truck one color. I have not seen any rust through and the 'then rust' seems to be contained. I always thought that I could sand blast or somehow get that rustoleum off and repaint.
It now is dull and faded. If you go that route, I recommend you thin the paint. It will lay flat but you should put on a couple of coats.
