You have two coils in the A/C unit, the condensing coil and the evaporator coil. Your evaporator needs to be cleaned. If you look at your A/C unit from the out side, you will see a coil, that is the condensing coil and it faces the back of the camper. If you remove the cover you will see the evaporator. Be carefull with cleaners, once you apply the cleaner it must be washed off. They do make a cleaner just for evaporators that are self rinsing when the unit is running. The evaporator stays wet when the unit is operating and this is where the condensate comes from, once you turn the unit off the coil will air dry, as it drys it collects dirt and dust over time it will build up and then it starts to smell and it is a good foundation for mold to grow, damp, dark and warm after the unit is off for long periods of time. This is can be a helth issue.