I have some cracks in my '90 Excella 34' end caps as well, front and rear. I have owned the trailer for 3 years now, and they are about the same size as when I bought the trailer. I pointed them out to P&S when I dropped off the trailer this fall, and they have seen it over and over again. I am going to consider it part of the "patina", and not worry about it.
One other point, the end caps yellowed over time. The PO had new drapes made for the entire trailer, the really good ones, and chose "gold" color. It ends up matching the end caps, so I do not need to concern myself with the yellowed end caps, they match.
"I've got aluminum fever, and the only prescription, is more AIRSTREAM!!!"
'64 Safari Resoration Blog ("May"):