Originally Posted by cpaharley2008
These heaters operate off 12v and should only be used while you are hooked up to electric in order to keep the battery from discharging
I don't see any point in 12V tank heaters if they can't be run while towing; if they can only be run while on shore power, they might as well be 120V AC. Of course you wouldn't want to run them on just the battery, but while driving the charge line from the tug can provide up to a few hundred watts to cover the heaters.
Dual-voltage AC/DC tank heaters are made for use on and off of shore power.