I mentioned this before but all epoxies are pretty poor in UV resistance and all have a tendancy to yellow fairly quickly.  Ever wonder why you never see pure epoxy paint for exteriors?  There are some hybrids using acrylic and epoxy (acrylic is excellent in UV, just look at the way Plexglas lasts which is of course acrylic and is the backbone of house paint).  But even those are rare.  Glad you tested it though Ed.

 

Dan Newland