There are tank pads made for 12V, 120V, and some combination 12/120v. Some have built in thermostats, some don't.
I have the 12V version installed (from the factory) on my tanks and drain pipes. They will drain a battery, very quickly. On the road, I use them sparingly, and shut them off during stops that may last more than an hour. On shore power, I can leave them on. Mine have the built in thermostat, that turns the heat on at 43 degrees and off at 44 degrees.
18 Nissan Titan XD
12 Flagstaff 831FKBSS
Wife and I
Retired Navy Master Chief (retired since 1995)