I can tell you the base of the bay is fine. The trim I am sure is not
painted on all sides other than the cut and splice sections I have done
myself. The trim is not sealed to the base very well. The trim is
definetly not shaped to shed water. That is the nature of most bays like
mine. They do not shed water well. This a big reason why I want to use
some kind of synthetic trim. To keep the bay to look the same, it will
always have a problem with water. Placing a small gutter around the top
may help, but the expansion and contraction due to southern exposure is
an issue. In a perfect world where the trim and base are kept totally
sealed at all times, I might be able to keep everything intact. But that
seems near impossible as I have tried and the problem persists.
Bernie

wrote:
If the problem is limited to the trim and the basic structure remains
sound, I would make the following set of guesses:
The trim is not painted on all faces before installation.
(This includes the cut ends.)
The trim is not sealed to the body of the bay or the sealant is not
maintained.
The trim is not shaped to shed water.

I would * not * wrap the trim.

There are a number of synthetic materials that one might use.
The first that comes to mind is fiber-cement.

Tom Baker