30 to 50 adapter feeds both legs but only 3600 watts is available assuming zero voltage sag from 120 volts.
I'm pretty sure my autoformer would get a *real* workout running two roof air units from a 30 amp shore power supply.
If you must do this--then at least monitor the voltage. When it sags below 107 it is time to reduce the load--or add an autoformer, or both.