12 volt generator is also an option
Depending on your house bank size, you also might consider a 12v generator. I have a similiar sized boat (40 ft with a 16K and 7K A/C units plus microwave and 900 ah house bank) and did a fair amount of thinking before deciding on my generator. I ultimately went with a Panda 4000 AGT (4kW but DC at 14 volts). My rationale was as follows:
1) sleeping at anchor with A/C if truly necessary only requires the 7K btu unit which is in the aft cabin and runs on 7amps @ 120v
2) I can run the aft A/C unit off the house bank for the startup to get past the surge requirement--comes out of the battery bank--and then the generator kicks on when the house bank voltage drops as below in #3
3) the Panda 4000 AGT generator can be configured to turn itself on when the house bank voltage drops below a preset level
4) "Loading" the generator appropriately isn't an issue because it runs at a variable RPM to match the load--no need to worry about a fixed RPM of 1800 or 3600 to match the 60Hz cycle of 120v output. Since the generator runs to charge the battery bank and not to match some load, the generator is always appropriately loaded (and more fuel-efficient than a 120v generator supposedly).
5) battery charging is quite rapid for the bulk phase as the generator puts out 280-320 amps DC at 14 volts (of course configurable for battery type).
I don't mean to sound like a salesman (I'm not) but I really really like this generator setup. Of course, this whole shebang is predicated on a large battery bank that can accept a large charge current (I have Lifeline AGMs) and a large inverter that can run the A/C (I have a Freedom 25 and a dedicated 3000watt/5000watt surge inverter for the A/C units when not on shore power).
Just another option to think about depending on your needs.