I’ve not had the opportunity to cross brands but I’ve paralleled Honda EU1000, 2000 and 3000 generators and found that contrary to common speculation, the smaller one doesn’t quickly overload, the bigger one covers more of the load.
Buying parallel kits is a waste and not even as good as making your own.
All it is is wire. The 120VAC outputs are simply connected together.
I use electric outlet boxes. I usually fit them with an RV30 camper type receptacle and a twin regular 20-amp outlet. To be really tidy I’ll use two power tool replacement cords to connect to the generators because they have nice molded in plugs on the ends but sometimes I’ll just use chunks of a discarded heavy duty extension cord that had damage somewhere and put some male 20-amp plugs on the ends.
Use strain relief grommets where the cords go into the box and you’ve got a very “pro” parallel box.
I’ve thought about even adding a circuit breaker but it’s unnecessarily redundant, you’re already feeding through the ones on the generators.
