Tracking down the cause of damp problem

merlin7835

I have just bought a 1995 caravan which appeared to be dry but having bought a damp meter I have detected damp in the base of the back cupboard outside the toilet and also at the base of the post which supports the wardrobe - but cannot find the source. There is no water on board and the roof is dry. There doesnt seem to be any pipes it could be coming from and the toilet compartment is a sealed unit. Please has anyone got any suggestions where it might be coming from? thanks