Let’s start by wiring up a simple breaker.
Yes, we know from experience that some one will come along an throw both breakers up at the same time, and we’ll have trouble (likely smoke). With this situation understood, we add a simple interlock.
In the above example, we must move the bar to the left or right and align the slot in the bar with the switch or breaker we will operate.
Shown above is the simple DIYer Transfer Switch Box I recommend making. There are a number of reasons, one being the price of $12, another is the fact that the Square D home series of breakers boxes will accept three different brands of breakers. When you find the more flexible box at a lower cost, you should consider it.
Transfer switches with interlocks can save you a lot of trouble as they can be used for a lot of things, and need not cost a lot of money. Make the plate yourself, or add $6 to a PMG order and get one from me. I suggest 10-32 screws for mounting. Home Depot is one store that carries the Square D series home boxes.
Will this setup pass your electrical codes? I’m told that in some jurisdictions, breakers are not accepted as ‘switches’. If you want to be legal, do some checking on your codes.
Tying your inverter and generator together is a bad thing, providing an interlock is important. I’d rather have one that didn’t meet a code than none at all, but you will always need to consult your local experts.