I'm planning to put up some crown moulding on the screened in
deck, but instead of having it attached to the wall and the ceiling, I
olan to drop it a few inches and drop a string of led lights to
generate some "mood" lighting.

I was talking to the builder of my house about this project and he
suggested I use extuded styrofoam crown moulding. It would be easier to
install - only some form of calking with brasds and since the project
was outside, the styrofoam would need less maintenance than wood.m
required. However, he was unable to provide me any sources for the
product that wasn't an elaborate design - our trim out there is simple.

Could anyone provide the name of such a source?