Wire inverter to existing transfer switch or need another?

They do make 3 way (or more) transfer switches so that you folks know I've seen a 3 way. But as I said above if you get a Inverter/Charger combo it has a built in transfer switch like a UPS and then you add a sub panel and run the outlets from the sub panel instead of the main. >Works great Trust me on that. (Till the inverter fails that is. but that took a long, long time).