Most boat A/C are 16K, so thought the two in parallel would run them. __________________
The problem is seldom in keeping the units operating , its starting the second unit.
The soft start kit might help , but if you are contemplating purchasing an inverter , getting one that will assist the AC system does work well.
The start (LRC) current is only for 1 second or so and will not run down the battery a substantial amount.
This same system , a passing thru, boosting inverter works well at out of the way locations where 15A of 120V is all there is.
With big batts an almost normal lifestyle can be had with the house batts catching up all night. NO electric stoves tho,