When I mentioned AC Freeze-Up, I incorrectly suggested the freezing happens at the condenser in front of the radiator. The freeze-up happens on the "heat exchanger" (evaporator) inside the HVAC unit in (or near) the cab. The heat exchanger is chilled by refrigerant, and the warm, moist cabin air passes through the AC heat exchanger, and moisture in the air condenses on the surface of the heat exchanger as the air is cooled. That enables the AC to dry the air. That's why a typical air conditioner in a home has a drip pan and condensate drain.
If the amount of moisture is too much for the system, the condensation will form a layer of ice that eventually prevents air from flowing through the heat exchanger. I can't say for sure, but I believe fan-forced air is able to bypass the heat exchanger, maintaining air flow, but the air is no longer chilled. The only solution is time to allow the ice to thaw...or, depending on the design of the system, add heat from the heater to melt the ice. (This depends on whether the heater core is before or after the AC heat exchanger.)
Since you are attempting to cool the cabin area of a motor home, it's possible that you may experience a situation similar to a regular house. Like a house, there is a LOT of warm, moist air in a motor home. In the cab of a pickup or cabin of a car, there is far more limited air volume to chill and dry. If set on "recirculate", once cooled and dried, the AC doesn't struggle dealing with moisture. But, if your driving cab in the MH isn't isolated from the living quarters, the volume of air to be chilled and dried is comparatively enormous. And if the "vehicle" AC system in the MH isn't scaled to cope with this, it could be overwhelmed pretty easily.
Again, I'm assuming that you may be dealing with hot AND humid conditions...not typical hot, dry conditions found in the SouthWest. If so, as you prep for departure, with doors and storage areas wide open to the outside air, your MH may intake a huge amount of hot, humid air, and the vehicle AC may simply not be up to the task of cooling and drying it all before inevitable freeze-up.
If any of this makes any sense, perhaps you might prep the camper in advance, then close up, connect to shore power, and run the roof-top AC unit(s) full blast for a while to get a head start on cooling and, especially, drying the air before you take off on the road. And, while driving, try to avoid introducing outside air into the cabin at pit stops, etc. Keep the doors and windows shut, and plan your entry and exits to minimize "pumping" outside air into the cabin when opening and closing doors. Each time you open a door, it sucks a huge amount of cooled, dried air out the bottom of the door opening (cold air sinks) and replaces it with warm, moist air at the top. And when you close the door, it happens again.
All this yammering may not describe the source of your problems. It's just a hunch. This video shows how the AC system works, and when you look at the image of the evaporator (heat exhanger that cools the cabin), you'll see how easy it can be to have it freeze up with a coating of ice under the right circumstances.