If they're like the ones on my Georgetown, they are only applied to the black and grey tanks. There isn't one on the potable water tank. We bought the rig used and the original owner chose them.
According to the manufacturer's documentation, they are controlled by thermostats built into the pads. The temps at which they turn on (at 40F, falling) and off (60F and rising) are not adjustable. Who wants to heat the sewage up to 60 degrees?!
They are 12v DC powered and draw 7 amps each. My installation has two on each of the waste tanks. It doesn't look as though there's any overheat protection if they get turned on with the tanks empty, and I'm concerned about possible melt-through of the tanks, with 84 watts of power going into a fairly small area.
I think, at best they're not much use, and at worst they are potetially damaging. Since we don't use the RV in cold weather, I've disconnected mine.
Frank and Eileen
2 Labradors, both yellow Males - Bailey and Angus. Both rescues. Angus will be 13 in Jan '15, Bailey is 12.
Our MH is an 02 Georgetown 325, F53 V10, now on consignment with a dealer.