The one thing I would check on the other battery is how much current it will accept from a discharged state. Some batteries can accept a boatload of current to charge quickly and alternator, voltage regulator, and wiring will need to be within spec. if that is the case.
An alternator is not technically a battery charger.
$150 for the charger might be cheap insurance to lessen the load on the truck and it's components.
Lose a charger and worse case the house battery is not charged, lose a part on the truck and you could be dead in the water wherever you are.
This may not be the case at all (as I don't know anything about the 3500 diesel truck itself), just something that I would check if changing to a different type of battery.