Johan solution is something I would do because I totally dig the custom design stuff..
there are also some new solutions out too. which are 110 volt A/C when parked and road A/C when on the road..
I dont know ,much about them as my busses are pretty much always running if im in them so I only set up road A/C..
these are not plug N play systems, these are components to a system that needs built. i will say ProAir will help you design a system but it is a bit outside the box for them as they do alot of contracts for stabdard systems and also manufacturers of vehicles come to them.. however if replacing your existing systems is in the mix then these inside units might be of interest.
this is a system of sorts.. I have worked with a gentleman named Jeff there.. theres a level of skill required to install and bring up a system like this.. (im a former HVAC engineer so it all comes easy for me.. well sort of anyway ha! A/C always throws curveballs)
12 volt / 110 volt system..
https://www.proairllc.com/313-110-12v-w-106-condenser/
I know space is a concern for a lot of people.. or logistics (tall people bumping heads on ceiling units).. thus why mamny people remove the factory A/C..
thing to think about is the typical school bus has 100,000 - 140,000 BTU of A/C.. thats right enough A/C to cool a mansion or a small offic building..
now granted you will likely insulate your floors, ceilings, walls, windows.. or remove some windows / replace with nice RV windows, etc and not need that much A/C but it takes a lot more A/C to cool a bus going down the highway than it does to cool it when parked.. you may insulate and find that you dont need the rear system and can run just the front one, or you may want both.. or you may be taking the bus to alaska where you dont need any..
I just always ask people to think before tearing out heaters and A/C's that came with their bus.. they are usually somewhat costly to add back in once removed as parts get damaged / wiring and hoses cut, etc..