Truck Camper severe water damage rear wall

Driver's side lower rear sounds like an issue I just had. The damage I had was on the passenger's side due to the Happijac wiring. The wiring connector should be installed with the wire coming up from below. Mine was installed with the wire entering from the top. A small crack developed and water entered the connection box and had no where to go except through the wiring hole into the camper. The water rotted out the upright and one of the horizontal supports. It took me two full days to repair. I suggest you start digging and find out what is rotten and needs to be replaced. With luck the skin of the camper is ok and you can slowly remove the inner rot and replace the pieces. With luck this will be tedious but a low skill issue. If you pay to for someone to work on this for a day or two, plan on paying many hundreds of dollars for even a relatively simple repair.