A light metal chain with small lock would be a most simple solution to protect the panels. however, there are some high tech solutions too. I've seen some portable battery powered cameras that can send instant notifications when a thief came, or sound a high pitch buzzer. Those are pretty nice. By the way, I've found this article explain the different options that we can use to protect our solar panels from stealing. Maybe, it will help you too.
I've used a portable Zamp solar panel to supplement my ETI roof mounted panel for years. I lock it to the trailer with a cable tether. I've never had a problem with it walking off. The only thing i've had taken in 50 years of camping was a Texas flag we were flying at the camp site.
Trailer: 2016 Escape 19 Chevy 2012 Express 3500 Van
Posts: 1,753
A masked bandit stole from me.
Years ago, we left a cheapo Styrofoam cooler on a picnic table in a state park......overnight. Those bandit raccoons didn't need no stinkin' bolt cutters for that one. I seem to recall they just tipped it over and absconded with breakfast, lunch and dinner.