I haven't got a figure for the maximum laden weight of a 1994 Swift Rapid 450GXL but my sources tell me that the unladen weight is 1000kg. The 2.0DTI Zafira which you are talking about is the old model and that only has a maximum permissible towload of 1050kg, so you haven't got much of a margin for putting anything inside the caravan before you'd go over the limit. You would certainly not be able to make full use of its maximum permissible laden weight, which is probably in the order of 1200kg. So, it's got to be either towing a nearly empty caravan or a new Zafira or some other towcar.