I don't know what the percentage of opportunistic thefts would be as opposed to premeditated thefts.
The opportunist would possibly be deterred by chains and locks, particularly if there are other folk around, but the @rsehole who got up that morning with the intent to go out and pinch somebody's camper will undoubtedly be well prepared with the necessary kit, including a big pair of bolt cutters.
I guess it comes down to where you park your trailer. If at home, and accessible from the street, maybe something like turning the trailer around with the hitch facing away from the street, and using two wheel clamps, because if the thief has cased your place first he will come with a Jack and if you only have one wheel clamped it's only a couple of minutes to swap the clamped wheel with your spare.
I've read of campers and vans being pinched in broad daylight from van parks, so fitting something like wheel clamps will make your unattended trailer look like a much less attractive proposition.
Free camps would be a different kettle of fish. If you had been there for a day or so with other campers it may be OK to go off in the tug for a trip if you make arrangements with someone to keep an eye on your gear while you are away, after having discretely noted the rego numbers of other vehicles at the site.
The other alternative is to fit a GPS tracker. It won't stop your trailer getting nicked, but it may help you to recover it before it has gone too far, or been stripped.
Always remember the old saying that 'locks only keep honest people out'. If a determined thief want's your rig, they will get it.
