If you are looking at a removable wheel clamp I would go for the Nemisis. It is very well made and easy to fit and is adjustable for different size wheels which may be important if you change caravans, like all good clamps it is heavy though.. There is also a Nemisis Ultra which is light and easy to fit and very good if stopping on a motorway services as can be fitted in seconds.
Unless your insurance requires it I would not bother with a hitchlock. Thieves can by pass them easily by chaining the caravan to the towing vehicle or by fabricating a frame to fit over the caravans a frame. In both cases they can drive away without removing any hitchlock.
Whatever you buy go for one that shows the Sold Secure preferably gold logo.