I have a couple of concerns...
1. The roof is slightly arched and the panel is so long it will be high centered. Any suggestions?
Can you mount the panel long ways on the roof? I mounted my panel that way, it worked great. I put rubber between the panel and the high point of the roof, so that the panel would not dig int the rubber.. It is working great.
2. The panel Z brackets or whatever I use will need to be screwed into the trusses, or just the 1/8" plywood under the rubber membrane?
I installed 8 "Z" brackets and they fit perfectly... here is the link to the website for an adjustable solar panel mount.
They should meet your needs better than the "Z" brackets.