From the added info in your second post you are needing 120VAC for the ferry to FL.
There are two solutions. Do nothing. A fridge does not go hot the moment that it is unplugged. Assuming that you will be using CGs each night during the ferry the fridge will chill down each night. Keep the doors closed all day to lose as little chill as possible.
Second option is installing an inverter to run the fridge on while travelling. The TV may or may not keep up with the draw of the inverter but starting with a charged battery overnight the inverter will give some hours use before the battery goes below minimum voltage that the inverter needs. Be sure that the inverter is feeding nothing but the fridge. No other draws.
An engine turning 1800rpm plus at highway speeds should be producing maximum charge to the battery however the issue is long thin wires to the trailer battery which produces VD & a low charge rate.