Here is how I ended up doing it. Similar thought, but low profile and easier to mount. My CTC is 7ft wide. I bought 8ft 1 inch aluminum channel and cut it to 7ft. I spaced them appropriately and bolted them down with one self tapping screw on each side to the outer frame using Dicor tape underneath the point of engagement to seal. I then made L brackets and screwed the panels to the cross members in 4 places front and back. Works great and minimizes screws into roof.
Here are a few recent pics of my 5 100W panels after I painted the roof with Henry's Roof paint.
Three cross members and only 6 screws into the roof on outer edges into steel frame to minimize impact and opportunity for leaks. Panels double up on the middle crossmember.
I also mounted them front and back like I did with the brackets dropped down to keep profile low and close to roof. There is little to no air getting underneath to create lift and stress on the highway. It has been a few years now and no signs of any movement or stress.
A closer look how I mounted with brackets I made from 1 in aluminum angle stock as I was installing. Just cut 4 inch pieces and used them front and back to set on crossmember. It allows the doubling up on center crossmember. I did push them together before I screwed them down. I was just sizing it all up in this pic.
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