Polyester Primers

ok,one more question:Is a Gallon enough for the Duster?How many coats can I get out of the gallon?I know it mixes 4:1.Ive done this before with good results:Block dry with 180 or 220,spray guide coat,wet sand with 320-400 until the guide coat is gone.It takes awhile to sand out the 220 scratches,but I usually did it that way to avoid having to spray another coat.Seems like a shortcut ,but always worked great.I wouldnt do this on colors that show scratches easy though(like metallics)but since my Duster is going to be a solid color,I figured it wont hurt it.