Some pics of the awning install. I spoke to NRC on the phone and they were lots of help locating the top rail. I was told that I could locate the track anywhere I wanted to vertically and did not have to attack the track to a horizontal member. They also told me that the vertical frame members are on 16" centers and that I should be sure to screw into them anywhere the track crosses one. I screwed the rail on using the pre-drilled holes then went back and put additional screws into the vertical frame members. The rest of the install was per Dometic instructions.
P.S. I used a magnet and tape measure to find the steel frame members.