Wow - lucky break GQcamper! The sight of a 6ft tall, 130kg, naked guy still half asleep swearing loudly as he barrelled across his lawn in the dark with a hastily picked-up golf club must have convinced them that it wasn't a good idea to stick around!
As GG rightly says, if someone wants something bad enough then there's little you can do to completely stop them, the trick it to make it harder/noisier than your neighbour's. I like the idea of a motion alarm, but my dogs (or the neighbourhood cat who thinks he has run of the place) would probably make a game of setting it off. I've been thinking about either a wheel-clamp, or just a big hefty length of chain that can be run around the axle and through a wheel, maybe around a pole of the house/fence as well.
Not that anything could probably be done now, but have you at least reported it to the police? Even if they don't send someone out, they can keep track of what's going on around the place, what items are on someone's "hot list", etc.
I hope you have fun on the weekend, and don't spend all night worrying that someone's going to try to flog your camper while you're sleeping in it!
Again, well done on disturbing them! Shame you didn't catch up to em.
Matto