You may find that as your caravan is over 15 yrs old the wiring never took into account the modern usage of RCDs for caravan sites now.
It is possible that there is a fault on it that will be picked up by a RCD, which may not have been picked up previously.
If the caravan as been stationary a while then dampness may have got into the wiring and again this could be tripping the RCD.
Again if it's been staionary for a while there could be some rodent damage to the wiring, the possibilities are endless really.
IMO as it's such an old installation I would get an experienced electrician to go over the system for you and check everything out.
It is recommended that as a minimum a caravan should have a Periodic Inspection every 3 years and if the usage is "frequent" then yearly, and if you have not had one done. it may be the best course of action
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