Do you have a note of the key number, or is it in any of the caravan documents? How old is the caravan, if you contact the maker with proof of ownership they may be able to provide you the required information. From your note it looks as if you have different keys for the storage box compared to the door, or thetford box. Without knowing the alarm type and caravan type etc its a bit difficult to advise more precisely. My current car only came with a single remote and by looking at its original documents I was able to obtain the info that allowed locksmith to make me another remote key, but he required the single key in order to copy the codes into the new key