If you are doing a frame and suspension parts, a quart of the POR15 is enough to do them all. I bought the POR15 and Chassis black to coat my street Ranger's frame and suspension parts from thePOR15guy on ebay (or some name to that effect). And I must say I wasn't too keen on painting it by brush, but once I started I found it flowed very well over the part and leveled itself very well too.
Of the quart, I still had some left over, but became unusable cause the little tiny bit that got left around the rim dried and permanently locked the lid to the can.
These pics are after the Chassis Black coat. The POR15 itself has a dull or flat finish.