Most likely it is not from water leaking but from age of the tape or ensolite. These trailers tend to sweat to some degree meaning moisture can from between the shell and the ensolite or what ever is applied to the shell due to temperature fluctuations and probably changes in humidity too. Propane
appliances can add to the moisture issue to some degree. If that is the only problems you see with regards to water leakage I wouldn't be overly concerned. It can give the trailers a musty smell if not aired out from time to time. There is a buyers checklist Ian put on here for some crucial things you do want to look for with regards to the frame, axle
, door fit, etc. but I think it applies more to Bolers specifically but some good info to know.