Roy,
You can rinse the condenser coil from out side the coach, but be careful not to bend the fins with too much water pressure, and also be careful not to spray water on the rear outside corner of the A/C unit where the circuit board is located.
The evaporator coil can only be reached through the access door in the basement wall, but it would be very difficult to wash that coil without doing more harm than good. However, if your filter is installed in the coach floor behind the grill at the end of the kitchen counter, it would be a good idea to at least check that coil because if the area that the A/C unit sets in is not completely sealed, and many are not, that coil may be very dirty. If so you can use a fin comb for excess material and coil cleaner with low pressure spray. The water will drain out under the coach through the exhaust air port if the water flow is not too high.
My preference is to install an 18 by 36 filter directly to the evaporator coil side of the A/C unit if it does not have a return air duct, and in that case the filter is in the duct itself and changed from outside the coach.
Gerald
