[rowmanholiday]

The only things I would add to the advice listed above is to put more than one coat on it. I personally would put a minimum of (3) coats. You will want to wait for them to dry betweeen coats though. And if your metal surface permits, I would use a paint roller whenever possible and a brush around the vents and such. The temperature when applying your coating can make a big difference also. I would pay attention to the range limits that are usually listed on the can.
And of course as was said before, prep is indeed the key. The better the prep, the better the end result.

Good luck!