there are a few ways to mount panels to the roof, but as i do it for hire, I use uni-strut.... its a clean low profile installation.
the layout is made where I want the mounts, then I pressure wash the areas and wipe it down with acetone..... then i make my precise marks where i want the mounts located and lay a heavy bead of Dicor Roof Lap Sealant the entire length of where the uni-strut piece needs to be located.. then i press the uni-strut into it, and use a couple of 3/4" screws to mecanically attach the strut to the roof, and cover these screws with sealant.... then i dress up the caulking so that there is no place for water to set in a divot, and once the roof sealant cures, the mounting structure is firmly attached, and no place for it to ever leak.
I use the 11/16 high uni-strut, and after the panels are bolted in place, the top surface of the panels are about 2"high off the roof... low profile so that very little wind can get under them....
the roof structure is "laminated", as in thin plywood, so there isnt much to grip with a screw, but the rubber membrane is adhered to the plywood and the plywood is adhered to the trailer, so as long as you have sufficient surface area, the panel mounts being glued down would either have to lose their adhesion and peel up, or the rubber roof would have to lose adhesion and peel up "all at once", because its a rigid structure after its all installed and it cant start to peel up at a corner and slowly get worse, it STAYS PUT...
the screws add a questionable amount of securement, but they do keep the rails in place until the sealant cures.... ive never had any of my installations fail, but then it really doesnt take much to keep panels in place as long as the wind cant get under them with enough force to cause a lifting or buffering/vibration action.....