I guess theft is always a possibility. I don't think many have had a problem with theft of solar
panels. Might be more of a problem if your trailer is stored or you tend to make day trips leaving the camper unattended in rustic locations without other campers about.
Think if they have to use tools to steal it making them bring a step stool is not that much additional burden.
Suppose if one had a bolt hole with a lock in it that would make it harder to remove. Or even just an odd ball fastener like torx would be enough to slow them down.
Good to know your getting excellent use of that back bumper :-)