I have a red dot roof top unit in my 110 csw , I fitted it when I lived in OZ , what I saw with regard to factory aircon in 4x4 in extreme conditions confirmed what I had decided to do .
The roof top unit is what is used in commercial applications eg on bulldozers , road trains , graders etc .
The basic reasons for that unit choice , in conditions where you want max cooling so does the vehicle , so putting a condensor radiator directly in front of engine cooling radiator not a good idea , most (read all) 4x4 have to turn off aircon to allow enough cooling to engine when operating at high load eg in sand dunes, towing heavy trailer etc, in 40C+ . Some even when on hard surface during long climbs .
Mine will also take in filtered outside air to pressurise the vehicle so that it keeps bulldust out , standard vehicle aircons have to switch to recirc in dusty conditions and so cant pressurise against dust entering elsewhere in vehicle . It has kept vehicle interior cool in 45c+ and its still not at max output , and thats in a csw with a V8 .
You can get a whole range of systems from red dot, its very good kit . HTSH
Forgot to mention mine is the 9727 unit