I installed fiberglass new construction windows 15 years ago on the front of the house. I used finger-jointed casing around the windows that measure about 1-1/2" square to fill the cavity around the window. The tops and sides are pristine, but the bottom pieces are crumbling! The eaves protect all of the upper wall and casing, but the lower wall takes a tremendous beating from rain and sun. Bottom line, I'm looking for a material that will hold up better. Thinking vinyl, but not seeing those dimensions without building it up. Starting to think about some sort of vinyl or composite wood decking that I could rip. Any ideas? thx!
Your best choice would be something made from PVC sold in the trim section of any usual big box home improvement store. Or you could use a heavily treated wood like "Armour" wood that has a higher resistance to rot which is also sold in most stores. Also make sure to use proper flashing behind the trim.☺