I used galvanized steel duct pieces from Home Depot. They are ment to form a round duct of various diameters but I just put them into a 1/2 circle, you could do smaller ones as a 1/4 round. They are pretty strong and in my case worked well because I could reach up inside them and latch/unlatch the front window shade.
here's what I was trying to help, those sides stick out even further then they appear in the picture but especially behind where the top sides of the tow truck taper.
