Outage backup (120 and 240) in grid-tie system

Tricksailing said:

I'm installing a grid-tie system in Baja Sur, Mexico and would like to include an emergency back-up for the not-so rare power outages triggered by storms. In some cases outages have lasted for days.
The most important appliances are refrigerator/freezers but it would also be nice to cool at least 1 room with AC and keep the water pressure boost pump running, both of which run on 240v.
I'm considering a Sunny Boy (7.7) inverter to take advantage of the Secure Power Supply (SPS) with a generator to take care of nighttime consumption. Are there other options I should consider?
A problem with the Sunny Boy is that the SPS is only 2 kW which would be pushing things to run a 1.5 ton AC along with a couple of refrigerators. The other problem is that the SPS is only 120v so would need a step-up for 240. It doesn't look like SPSs from a pair of smaller Sunny Boys can be synced for more power/volts so I suspect a step-up transformer would be the solution for 240v.
It would be nice to have the system hooked into the house wiring (with appropriate interlocks to keep power off the grid). I'm envisioning a 120/240v center tap transformer (or a pair of 120/120 transformers) hooked into the SPS with a grounded center tap to mimic the house supply. Is this possible, or would issues of inbalanced loads on the 120 lines create too many problems?
As I noted above, I'm still planning this and am open to alternative suggestions.