... Each of those draw 9 amps as I recall. So to keep two running I would need 18 amps and that is a 2.2KW. To run one and start the other I would need 18 amps start-up plus 9 amps to run or 27 amps from the inverter. That translates to 3240KW for the inverter capacity. ... What am I missing?
I think your numbers are off.
My 13,500 BTU/hr units draw about 13 amps each steady-state in average temperatures (more in sweltering heat, and a bit less in more temperate conditions). They call for 20-amp HACR breakers and draw at least that much at start-up. To run two of these would require a minimum 3.3 kW inverter -- 3.0 is too small. Practically speaking, the next size up from 3 kW is 4 kW.
BTW, as I wrote in the other thread, I ran two of these A/Cs just fine on a 5 kW generator. At 20 amps each for startup, even if they start together that's 4,800 watts. It was a little Onan Marquis on a Fleetwood gasser. I didn't call you on the 6.5 genny because you told us not to... for all I know, you have a 3,600-watt battery charger that runs every time the generator does (not an uncommon configuration), which would leave you just 2,900 watts for your air -- not enough, as I just described. Now, if you want to discuss that problem, we can, although perhaps a new thread would be appropriate.