Can you supply 20+ amps at 12V 24 hours a day from your battery bank? I can't. "Normal" power usage on boats is about 80 - 120 Ah per day, and your pump is taking 500 Ah.
Just to drive the heat pump you'll need nine standard 110Ah lesiure batteries, probably plus the usual four for other domestic loads ...
... and then you will need to replace about 700Ah daily into the batteries.
How many solar panels do you call "some", and what output do yo expect in early January when you need the heating most?