We are lucky I guess, one of the features that I wanted in a camper, was the ability to lock it up when we were away from it. The only thing that is left open is the tent, with nothing but bedding.
But when we were just tenting it I used cables and padlocks for everything. Real valuables were also taken with us.
If you can, use good quality padlocks on everything that opens and shuts. If this is too hard, use good quality cables and padlocks.
It may be a pain, but it beats getting stuff stolen and anything that looks too hard is more likely to be left alone.
For security when we are parked with the camper attached, I have drilled a hole through the pin and fitted a good quality padlock. This stops them simply removing the pin and sliding the hitch out. I also have padlocks instead of D shackles.
When parked on it's own, the chains are brought up over the A frame and padlocked under the A frame. A very heavy chain is run through the rim, over the suspension and padlocked. The Treg Hitch also has a pin lock.
So if they want it, they will have to put in the effort to take it. Then I have insurance that will cover everything we take camping.
have a good look at your Contents Insurance, ours covers us for everything, excluding the camper trailer. The Camper cover also covers us for the big ticket items that we take with us.