Wise Sales has their own parallel cable that can connect three Hondas, costs about 300 bones. Of course, via suicide cords, one can add more, but after four eu2000i models, I'd say the 30A connector will likely be saturated, even factoring in locked rotor amp current from compressors and microwaves.
This makes for some interesting configuration ideas. For example, the 1000 watt Honda and 2000 watt Honda will give about 2500 watts (guesstimating the wattage loss), which would be enough to kick off a 13k BTU A/C. For cooler weather, the 1000 watt generator attached to an extended run tank would help charge the batteries when solar isn't uable.
