Just to through a thought that occurred to me, watching hipsters convert Sprinter's into Eco-Glamper Virtue Vans..... and thinking as a person that likes camping in the woods rather then the de-forested flat lands of private or KOA "camp" grounds.... Why mount on the roof?
Yes, they are up and out of the way, no messing around with once installed. I completely get that. It's a vacation= do your best to do the lest.
But.... why not have the panels free to roam? Have them on adjustable legs to prop them up at needed angle. A long enough cord that they can be moved around to follow the one sunny spot shining through the trees. I know I avoid parking in the sunny spot so I don't cook in the camper, so roof mount would be kinda dumb in my case. Make a light storage case or sleeve. Stow them under the mattress for travel. In the back seat. Under the dinette.
IMHO, flat on the roof isn't the best when the sun isn't directly overhead.
Have a pigtail in a exterior storage cabinet or even in the battery box to plug the panels into. As a bonus, easy to keep them clean and avoids adding more holes in the roof, which is A+ on my list of don't do's if possible. Also, if they die, your next ones might not fit your old brackets. So now you've got pointless holes and some new holes to go with them. No thanks!
If the roof is the best place for them, either for sun exposure or theft deterrent, make a base (Plywood or ?) with rubber feet or silicone sheet thanks roof friendly. Mount the panels to this. You can still rotate then and you a cable lock to secure to a roof rail, ladder or wrap snug around a AC unit, etc. (Razor wire around the perimeter of the roof, while effective, might be unsightly and limiting in meeting new people. Unless you want to attract the weekend Rambo types....)
Just thought I'd toss that idea at you, in case it hadn't crossed your mind.