Can't help but think something's got to give here...barn with no power, boat with things drawing current all the time, no sunlight for solar power, no provision to charge whilst towing, not always time to charge when moved to launch...
Personally, assuming the barn's a given, I'd be looking to make the batteries easily removable and take home one at a time to charge with a smart charger. Then, switching all off on the boat except the tracker.
Solar panels - too expensive, too big for a useful output, unreliable weather. Wind turbine
Charging whilst towing - depends how far you tow, batteries still in an unknown state when you get there.
Better to start your journey with good, known batteries than arrive somewhere and find them flat