The paralleling or stacking with this type of converters is easy if one pick up a synchronizer pulse and output wave forms, since the electronics circuitry is simple .

A lot of hyped suggestions that one can place several in parallel or series ( stack)that theoretical can be done but in a practical way is not realizable due to the battery banking size.

Limit the stacking to 2 and choose the peak power from the beginning.
and be careful because if one is using a double stack like for 110/220 Volts and one is overloaded both can be damaged.

Stackable Inverters need current detection for each one and if one folds the seconds follow to protect themselves - if this capability does not exist then a good possibility of blowing both if there is a short in one lower voltage loop.

Voltage loop = in an stackable pair there are 2 lower voltage loops of 110 Volts and one higher loop of 220 volts.

DEMAND the specifications sheets.

They are not damage proof, fuses are normally used for ultimate protection NOT basic protection, so one may BLOW an inverter before the FUSES BLOW what they say is PROPAGANDA .