Trim coil is a plastic flashing.
We used an aluminum metal flashing that we found at the Socorro ACE Hardware. It was heavy for flashing, and BARELY the right height (this is why we ended up using the window frames). We had looked into buying sheet metal to cover the window frames and suffered from sticker shock.
Apparently the cost of sheet metal in Socorro was much higher than in other states. To have them cut the sheets to size doubled the price. We bought the flashing for much, much, much less $. We are frugal. And we wanted to keep the look of the windows (but not the windows) with the little awnings over them. These little eyebrow awnings have been used to shield vent covers from rain. We didn't want a smooth sided bus.
Skinning Over The Windows