Yep keep it. It is the most economical heat you can produce and as said, you can use it to cool. A small heater
won't do that. Being so expensive to install one, it would make a great selling point for your boat if you ever bring it to market. If you have a genset, you need to run that to charge the battery
system. Having the AC on while dong so, just makes use of the excess power while the charger
. It can heat or sool and keep your boat that way for sometime afterwards, if you don't open the door that is.