On our older GT motor-home, they're on black and grey tanks only. The FW tank is in the living area (in a cupboard at the foot of the bed) and is considered warm enough not to need freeze protection.
We always drain the FW when the rig isn't in use. Since we don't travel in very cold weather, and overnight lows where we live are rarely below 25F, we've never used the Arctic Pack in the 4 years we've owned the RV.
After reading that the built-in non adjustable thermostats don't shut off until the tank contents get to 65F, I wasn't too keen on using the system anyway. Four heaters, each drawing 7 amps from the house battery system didn't seem to be a very good idea either.
Frank and Eileen
No longer RVers or FR owners