I read somewhere that narrowboats often have a second alternator fitted. For the leisure side?2001 Ducato alternator will have a decent rated current output - enough for what you want.
All you can really check yourself is the voltage which again should be high enough.
One advantage of old style alternators is that they don't have any fancy controls stopping them 'working'
I don’t suppose for a minute that this would be an option in a Fiat. So, taking a charge after the vehicle battery makes sense to me. Satisfy the vehicle, then the leisure side.