usual way for a rubber roof is to use "L" or "Z" brackets with screws and Dicor sealant
if you are implying "damage" as using screws then you will have a difficult time securing panels to a roof.
you could use an adhesive with a fiberglass or aluminum roof, but not for rubber. rubber does not have the tensile strength in a plane 90 degrees to the roof.
even if you did glue, you have no way to tell how well the rubber is secured on the roof, you could end up ripping off the rubber material under load from forward motion or braking.
I see! I was reluctant to drill holes thru the roof, sounds counter-intuitive but I guess its the only way!
My single 100 Watts panel is supposed to generate 5.5 amps max in the best conditions. I only seen it going up to 2.2 in direct sunlight, no clouds...that is having it canted against the trailer. Anyway, with the very slight electrical consumption (only a few LEDs for a hour max), that setup self-regen easy. Got the panel on sale for $200 Cdn..