Here are the industry reference points relating to moisture levels in caravans.
These measurements are ONLY for use with the Protimeter tester, not any of the cheap and cheerful, and very misleading, other makes.
Readings between 0-15% no cause for concern
Readings between 15-20% engineer to make note of readings and recheck at next service.
Readings between 20-24% possible early sign of water ingress, look for tangible evidence or ask for
Recheck.
Readings between 25-30% moisture evident, remedial work necessary, may not require stripdown unless surface damage (staining, pimpling and softness) is apparent. There is a risk of wallboard deterioration due to retained moisture in the structure if re sealed only.
Reading of 31% and above structural damage is occurring, deterioration inevitable, full stripdown of affected area is required
Whilst it seems very simple to get a reading and think you have a problem, it is not and other considerations have to be borne in mind when taking readings, such as ambient temperature, humidity etc.
Hope this helps