I did my trailer with Poli Glo when I bought it in 2012 and haven't touched it since. I just bought some more Poli Glo and am gonna do the front and rear caps this week. The caps show signs of the Poli Glo flaking and disappearing in runs from the top to the bottom - looks weird! It has not discolored at all and spends most of its time in the same orientation in the yard and gets sun on the back cap, drivers side and front cap. My trailer is aluminum sided with white paint - I only did the poli glo on the fiberglass - doors, caps, covers, etc. - and wax on the paint.
I'm happy...
Tim