Inverter feeding main panel-why not?

[Ozz]

I don’t want a sub-panel. I want the OPTION to have all (120 volt) circuits hot if I wish to plug something in, or turn something on.
If I want to plug a device somewhere that I wouldn’t have planned on with a sub-panel, I can use that outlet, or circuit.
I know the limitations of an Inverter on a battery bank, so I must be selective on individual, and multiple power loads.
I know there is a limited amount of battery power available as well.
The reasons I chose the Magnum MS2812 Pure Sine wave, is that it is a ‘Hoss’
It is 2800 VA continuous power (23 amps) 3900 surge for 5 seconds, 3200 watts for 5 minutes and a smokin’ 30 minutes of 3,000 watts surge.
All this at 90% efficiency with a small no load 30 watts stand-by.
I am using 6 Golf cart batteries.
The charging and Inverting aspect is an obstacle I am addressing.
As you know, you can’t charge the battery bank when you are Inverting.
I think I can use two relays, a 40 amp contact rating two-pole 120 volt coil for the Inverter charger power supply, then a small 120 volt coil N.C. relay to open the circuit to the 40 amp relay when it senses the power output from the Inverter supply.
The Inverter/charger on ‘Charge’ mode would have the 40 amp contacts closed, on ‘Invert’ mode, the contacts open.
All this would be automatic, a Ozz-transfer switch.
I could do this simply by flipping off the two-pole 30 amp switch I installed, or tripping the 30 amp supply breaker, but I want it to be automatic.
So, the only user select action would be the line voltage load management, I don’t think we would have any trouble with that, I have 3 wall-mounted displays that would be displaying the amp draw from the battery bank.
SO, why won’t this work? Am I missing something?