I have not heard of a problem with pine cone droppings denting or damaging the top of a TM. I can see being parked under a tree and hot weather causing sap to sprinkle the top or birds perching in the tree decorating the top with their droppings. Inconvient yes, fun to clean - definately not, but not causing "damage". As to the above natural coatings, I don't think TM fairs any worse than any other brand of RV. Owning a $500,000 Class A doesn't provide protection from tree sap and bird bombs.
Bill