I’m not yet a Nauticat owner, I’m a pilot. Proper fuel management has been for me a major concern for obvious reasons. Dip stick is by all means and always the best option. Let me tell you how I would approach the problem. I assume this option is available for boats too. Check for a fuel computer system, with 2 fuel tanks you need to have two fuel flow sensors installed to a fuel management system, that will give you the exact fuel usage/hr and remaining as well as fuel required to destination. Important is to install the flow sensors after the fuel has been properly filtered. But this solution though not necessarily cheap will give you precise figures even in heavy seas!
Otherwise most of the times the sending units are the big issue and corroded contacts (poor grounding).