We ordered the Arctic Pack with our Sunseeker 3100 and I've never used the heating pads. The furnace keeps the tanks nice and warm. There's a small flexible duct going to the utility compartment (sewer connections and shore line) and the compartment with the water filter and pump. We dry camped in the open at 19 F with a 20 mph wind. The next morning I checked the two compartments and they were about 50 F.
If you are camping where it will be colder than that or it will be below freezing for many nights heating pads are probably a good idea. Remember that the more water that's in your tanks the less likely they are to freeze. If you have sewer hookup fill them about half full and dump more often.
Of course, if don't use the furnace, or you set the temperature really low and keep warm with blankets, you won't be getting as much heat to the compartments and tanks. I have to keep the coach warm because I'd be in serious trouble if my dearly beloved's little dog got cold! Using up propane and running down the batteries are minor problems by comparison.
PS Check the location of your fresh water thank. In our 3100 it is elevated (above the grey tank I think) and there's no heating pad on it. The black and grey tanks are low and closer to the underbody seal sheet so they can get colder.