Thanks for the ideas guys, I'll give them a go.
I agree that the car is rarely left anywhere for any period of time, and whilst it may be easier to nick the whole car, it also stands out a lot more than 4 wheels in the back of a van. With a few weekends away booked, and staying in hotels where the car will be left out overnight, I thought £30 in the scheme of things was better than coming out and finding the car on bricks
Will have a bit more of a hunt round, but from the replies it seems most don't bother, so may not spend too much more time on it!
cheers
Dave