Our 34' has 2 AC's. Front is 13.5. Rear is 11.0. Even in 100° both AC's do not run all the time. It has 50 amp service. This allows us to run everything in MH without concerns of tripping a breaker. 50 amp service is actually two 50 amp lines. This gives MH a total of 100 amps.
Does Nexus connect both AC's to the ducts? This makes a difference in how well rear AC cools RV. As other have stated, We use rear AC during the day to cool and front AC to cool at night.
Adding a second AC and 55k generator is going to take away some load capacity on a E450 chassis.