[Daryles]

I used a stud finder to find the rafters when I installed my panels. Works great. Once I located the rafters I used blue Frog painters tape and chalk to mark them.
If I was doing mine again I would use unistruts as you are doing, then you can be sure every screw goes into a stud. I was only able to have the leading edge mounting feet on a stud.
When I determined where the mounting feet went I put down Eternabond. Then drilled a pilot hole, the put Dicor in the hole and where the foot went. Then mounted the foot and covered the screw with dicor. So far so good.
I may yet re-do my roof panels if I add more.
I will use aluminum unistrut and Renogy tilt brackets.