Some of our customers that have 2 A/C units designate just one A/C as the only A/C they will use when they're operating on their stand-alone 2,000 Watt generator. Their choice in doing this is a trade-off in the ability to run both A/Cs on a single 30 amp hookup – or on 2 generators in parallel, since not everyone can afford 2 SoftStartRV units.
If you intend to setup a solar type system with a single 4,000 Watt inverter to run both Air Conditioners, you would be better served installing a SoftStartRV into both A/C units. This way, it will not matter which A/C is cycling on at any given time.