Daryl,
Thanks for the response.
If I wasn't planning to use unistrut then I'd not be as concerned about finding the trusses. But the use of the struts makes it more likely that roof deflection could cause a screw to lose it's hold. However, I think strut channels offer far more advantages than disadvantages.
I used eternal bond tape in my last install just as you did to cushion the panel mounts against the roof membrane. That membrane is so thin I wanted the extra cushion.
I'm thinking that my stud finder might be flawed. I may try with another.
I really like the idea of strut channel. It minimizes the number of roof penetrations. I think 3 or 4 screws per strut would be enough if each penetrated a truss. It's also more scalable and modifiable. Adding or removing panels is much easier. If I sell the RV I can more easily take my panels with me while the next owner will have a system they can use. It lifts the panels a little more off the roof allowing for more air flow underneath and thus more efficiency. Besides, it just looks much nicer.
This video explains my ideas well
Thanks again
Tom