Hooked up to 30 amp will supply all your needs , battery size un important. Its the overnights on the hook you need to "size your batt " for. Here is a simple formula take your total amps per hr used (anchor ,cabin lights,refrig,radio (VHF & am-fm) anything that is a draw on your house batt. Mutiply by the number of hrs between charging
cycles (starting up the eng or firing up a small gen). This will give you amp hrs. This number should be 30 % of the total amp hr of your new batt. So if you use 90 amps hrs between charges you need a 300 amp hr batt. Caution there is a big difference between "starting amps or CCA cold cranking amps" and "amp hrs".