Poor ducting of the roof mounted units, is and has been a problem from the factory. Therefore, the added efficiency of the window units. We did not opt for the "window shaker". But, of course they would not be prone to the cool air ducting problems. Window and roof mounted units each exhaust hot air directly to the exterior.
Our unit is a "single hose" set up. I am not an HVAC tech, but I realize hot exhaust air, created by the compression/heating of the Freon, is vented to the exterior via a hose connected to an exhaust vent assembly. This is the air ducted to the exterior. It is exhaust air ONLY. This single hose does not exhale and then inhale. "Supply Air" ("make up" as you refer to it) is the inside ambient air of our RV. This supply air is blown over of the evaporator coils which becomes quite cold due to the drastic drop in temp as the Freon "boils", evaporates, when reaching atomspheric pressure, and this is what provides the cool air to our RV. There is NO outside/exterior "hot humid" air supplied to the unit nor any attempt to cool hot exterior air. If this is the basis of your "most inefficient type" statement concering our free standing a/c, your reasoning seems to be a bit flawed.
Believe you may be aware that the "Carrier AirV", for which you opted, recently had a Factory Recall due to a Major Defect and FIRE DANGER with the unit. I further believe that "Carrier" may no longer be in the RV a/c business. Perhaps "inefficiency" played a part in this unfortunate Carrier outcome.
If a second a/c is needed, I believe a good quality portable unit remains a prudent, lower amperage and efficient option. "Cheap" - not really.