Is it feasible to remove one or both wheels and replacing with axle stands when the caravan is stored at home - I am not convinced a wheelclamp and hitchlock will deter a determined thief
If you use winter wheels with locking wheel nuts that is probably better than a wheel clamp but you need to let the insurer know before doing that as some will not accept it. If they will not then one wheel with a clamp and one with a Winter wheel and locking wheel nuts.