There are many security systems available—Ring, Arlo, Eufy—that I know RVers use. Most, if not all, of those require WIFI, so that’s something to think about if you regularly stay in areas with no connection. I have a Eufy camera. It starts recording when it detects motion, and a light turns on. It connects to a base inside, so there is no subscription fee, which is a plus. Its just a camera, no alarm goes off (They do sell alarms though).
That said, oftentimes cameras, alarms, etc, won’t do much to deter a thief from a quick score. I’d recommend also getting a bolt down safe for valuables, changing the factory locks, and asking neighbors to watch your place while away. Nothing is fool-proof, but it all helps.