here's the 1/4" LUAN panels most manufacturers use on the roof...
https://www.lowes.com/pd/1-4-in-Laua...X-4/1000068895
also, another thought about Solar panel mounting, as I've done:
don't mount the panels each directly on the roof, instead build a simple aluminum 'frame' that each rests in, and the whole system can then be tilted together. One frame, and it can be built to mirror your roof truss measurements... if built from 'L' or 'U' channel, then your panels can easily rest inside the frame, and a simple zip tie thru each end can then 'anchor' them, versus a screw or permanent 'mount' for each....
just some thoughts... mine aren't anchored to the roof deck, but are mounted with simple zip ties on a set of aluminum channels that are themselves anchored to the roof deck with simple 'L' brackets, shallow screws, and silicone caulk.
I don't believe that solar panels, with their typical size and weight, are going to easily 'move around' while driving, at least ours haven't, in many, many miles. This makes also for a less permanent mounting system, and one that allows me to 'tilt' them if I'm parked for a good while, when dry-camping, or even to take them down to the ground if I need to. I ran my wiring down the rear ladder, thru the rear hatch, thru the chassis framing, and thru the fan outlet in the Inverter bay and into the neighboring Battery bay.... get 10amps for several hours on good days, whether traveling, or parked.