We have a 1991 30 foot dutchman camper with previous leaks?

My question is two parts. The side window and antenna on roof had leaks for the previous owner. The wall by the bedroom side door window feels spongy, but dry. How can you tell the extend of the damage? Also we would like to pressure wash the camper, would we be doing more harm than good? What should we be looking for as potential leaks?