Locating roof crossbeams for solar panel install?

I took off the roof vent trim piece inside the trailer, and here's what it looks like inside the roof:



I was able to stick a tape measure in above the insulation, and found the rafters are spaced 16 inches apart. Marked that off on top, and I could get one of the two screws in each bracket to go through a rafter. Used wood glue on the threads of all screws, and self-leveling roof sealant between the brackets and the roof, and over the screw heads. Hopefully that should do it :)