Should I use any kind of finishing product over exterior, red paint on a front door that is metal?  Client wanted a dark, barn-red color, and we know red tends to fade quicker than a lighter color…would a finishing product such as a poly or clear coat help extend the life of the color?  It is a metal door, which receives about 4-6 solid hours of direct sunlight in Phoenix, AZ, year-round.  Any instruction is greatly appreciated.