I have been in the RAC industry for 30 years and more.
Retrofit Cab A/C is a nightmare of a job. Even the best end up with pockets full of "Pocket Screws" and broken plastic when they have done the job. Me included and I work like a swiss airline Technician coupled with a swiss watchmakers eye.
I did once when we owned a Frankia Mercedes wire the Dometic Habitation A/C to a Pure SineWave inverter and contacter. Just as a belt and braces for use on the move if the cab A/C broke.
The Mercedes Sprinter condenser developed a leak whilst in Spain. So we managed to stay cool with the hab A/C ahilst in-transit. That said, our alternator was 220amps.
But, we also have run a small portable A/C unit whilst on the move in the rear of our first motorhome (Another Mercedes that we purchased with an already poorly installed retro fit cab A/C).
And the latter I would say is your best option !
You can use it on the move via an inverter and on-site when you are on EHU. Providing you have the space?.
I hope this help?
If not send me an email, same as my username but with @sky
.com on the end.
Happy & Safe Travels