No shore power at the dock?

You could fill the freezer section with "Blue Ice" bags and then take them out
of the freezer and put them in the refrigerator portion when you shut down, but
that won't be anywhere nearly as effective as running the compressor and
evaporator.

It sounds like you have an AC refrigerator,
no shore power, and you're setting the boat up to run your AC generator to keep
the beeer cold?

Or you've got a dual voltage refrigerator and the genset is running to recharge
your house bank?

A little more information might get you more helpful responses.